Upgrade time. I have replaced the hard drive in this build with a Kingston 120GB SSD + SATA to IDE adapter.
It works great, with DMA enabled in Device Manager and all that. I didn't do this for speed though, more so for the silent operation that an SSD provides. Also, these things are dirt cheap nowadays, so why not. I have formatted the SSD on a modern machine to align the partition properly. It should be noted that I'm only using 32GB of the drive, leaving the rest as unformatted free space in order to minimize wear and tear. Probably overkill, but I don't realistically need more than 32GB on this rig. About once per month, I let the system idle in the BIOS overnight as per these instruction in order to let the SSD's on-board garbage collection do its thing. No issues so far.
Additionally, the Hitachi CD drive was starting to have issues with reading discs, so I replaced it with an MSI 16x DVD-ROM. Drive noise is no longer a concern thanks to Nero CD/DVD speed (under Windows) and CDBeQuiet! under pure DOS. Both of these utilities can be used to slow down the drive to 4x speed which eliminates any noise that it produces while reading CDs.
Also, my Roland SC-155 is currently hooked up to this system (using the Fortissimo for MPU-401). Not sure if it will stay there for good, but it's working quite well so far.
The MPU-401 on the Fortissimo is completely bug-free, no hanging notes, stuttering, ticking and whatnot. Music wise, this system now covers quite a few things: from OPL3, CQM, AWE32, soundfonts to Roland Sound Canvas and even Yamaha XG. Here are some recordings from the SC-155:
Finally, I have edited the first post in this thread to reflect the latest upgrades. Extremely happy with this system right now. It's a nice, quiet machine for playing DOS and early-mid Win9x games. And for the more demanding titles, I have my AthlonXP rig which packs a lot more punch.