Hm why did you change the irq and hdma setting? Are you sure they
match with the settings of the game?
Maybe try with the default 3000 cycles or lower.

Yes, they are what matches the settings in the game. Before I changed the IRQ, the game would crash whenever there was speech at all. HMA I changed because there was an A:3 in the sound settings and I couldn't think of anything else that might be. This is the first game I've attempted to run under DOSBox, though.

One more thing, though... When I'm supposed to be getting speech, the music hangs for a second before picking up again just when the speech would have ended.

I only know the non-cd version of the game. Yet the music hanging might
be misconfigured sound.
Please try to change the dosbox settings back to the default (i7 hdma5)
and configure the game accordingly. Maybe you can post a screenshot
of the sound configuration dialog.

I have tried changing the configuration file back and changing the settings in the game, but it hasn't helped. Here are all the sound settings for the game in the installer:

Those don't look like DOSBox screenshots. Did you install the game in DOSBox?
BTW, I am not so sure if that game ever had speech for all NPCs. There are quite a few of them in the game, more than a hundred. The game data is not that big, around 22MB for both parts. Audio compression was not common in 1994. Most games used 8KHz or 11KHz mono 8-bit samples -- around 2 minutes/megabyte. Don't forget that World of Xeen is a huge game so most of that 22MB is used by game data. Even considering that M&M games were technologically quite impressive for their time I still doubt if they could cram a lot of voices. My version of game is M&M Trilogy -- I don't believe it is crippled in any way.

I installed it through the installer off the CD by clicking setup. The CD version of the game definitely has speech for all NPCs. I specifically remember a lot of them, and there's posts from comp.sys.ibm.pc.games.rpg around the time that it was released that mention speech for all NPCs. CloneCD says there's actually around 706MB of data for the CD image, which would be more than enough space for speech samples.

If you want to play it under dosbox, you should install it under dosbox as
well, otherwise the game configuration might be messed up.

I installed it again in DOSBox, and it hasn't made a difference.

CloneCD says there's actually around 706MB of data for the CD image

Is this in Redbook audio tracks or just plain data? If it is Redbook then make sure you mixer settings are correct -- just try playing it with Media Player or something. Sound card settings are pretty much irrelevant in this case but you may have to mount your CDROM or image with "-ioctl" switch.
This is really odd -- neither Trilogy nor MM6 Special (or Limited) Edition have NPC speech. So, New World Computing spent all that effort to produce voiceovers for all NPCs and used only on one edition of the game, apparently, not the most common (CD versions were not big sellers then).

The music itself is MIDI. Not sure what format the speech files are in, but they do not show up when looking at the CD in XP. Neither Winamp nor WMP11 can find them on the CDs. I am already mounting the CD_ROM with the -ioctl switch, since if I don't the game gives an error that says an audio CD is inserted.

Edit: Scratch that, WMP11 finds at least 30 voice tracks on the first CD, and they are definitely the voices I remember.

Does not sound like Redbook. Hmm, looks like at least some editions of World of Xeen were on two CDs. Curiouser and curiouser... I'll see if I can find that game but it may take a while.

I know the same version came in the Ultimate RPG Archive package, since I have it and it's two CDs as well.

Yup, I was just trying it when I saw your message 😉 By all means, Interplay did much better job than 3DO. I have all three of their RPG collections (the other two being The Ultimate Wizardry Archive and Forgotten Realms Silver Edition). As far as collection releases go, those are among the best.
Back to the topic. First of all, the game has NPC speech in DOSBox. Both WoX disks have Redbook audio tracks (~30 each) with NPC speech. WMP11 shows them and plays them just fine. There are a few unusual things about those disks. For one, the data track is nearly identical, only the label is different. Each disk contains a copy of the game, installer, and demos, including MM4 demo... The second disk is indeed ~706MB image, the first one is ~542MB -- my guess that the first disk has speech for Cox and the second for DoX. For some reason, the disk label is very long on both disks but DOSBox shows 8.3 label fine and the game seems to handle it properly.
So, theories. One is simple (but not very likely) -- check that speech in on in game "control panel," it is separate setting from sfx and music. Second is more complicated -- you are using disk image and something is not right with your CD-ROM emulation software (CloneCD? Didn't they remove emulation some time ago?) I haven't used CloneCD in years, switched to Alcohol awhile back, so cannot help here. The fact that WMP11 does not see audio tracks is suspicious. Try using real CD instead of image. In any case, DOSBox should work, you have issue somewhere else.

EDIT: Just in case -- I am using ykhwong's DOSBox 11/20 build.
EDIT2: Open your system mixer and make sure you CD Audio is not muted -- that setting does not affect WMP!

I am using the original CDs to play the game, I was just using CloneCD to find out the actual size of the data on the CD-ROM, since XP was only showing 52 MB and I know that wasn't correct. I also know that the speech in the game is set to on, since it's set to on by default. To clarify, my WMP11 did see the audio tracks when I switched it to audio CD mode rather than searching the disc for files.

So, did you check system mixer settings? That's pretty much the only thing left I can think of. That, and some odd setting in the game installer "Automatically adjust Sound Blaster volumes" which I set to "yes."

You mean Master Volume, correct? It is not set on mute. Besides, the music works fine. I decided to delete the directory and reinstall it entirely using DOSBox, and selected yes for the sound blaster volumes, but it still will not play the speech.

No, not Master Volume. Double-click on speaker tray icon and you will get to advanced mixer view with multiple sliders. One of them is marked "CD Audio." If you can't see it, got to Options|Properties and enable it.

None of them was muted, but I turned up the CD volume and still have the same problem. It's rather puzzling.

In older computer you had to directly connect the CD drive with your sound card to gain CD audio sound.

Maybe this is the case and the cables are not connected inside your computer?