Tbh, I wouldn't play Win2k stuff on a K6-3. It runs the OS fine, but it's underpowered for the games. I'd go for at least a P3 Coppermine. But a PCI sound card with EAX won't hurt DOS (hell, you don't even need to initialize it) so it doesn't hurt - by all means do it if you want.
As for DOS. You mention Tie-Fighter and MIDI. That means you'll hit the SB16 MIDI slowdown bug, so you don't want to use the AWE32 to host your DB50-XG. Apart from that you do definitely want 16b sound with those late games.
There's two ways to do that:
1) the commonest, SB16. That means AWE32 in this case.
2) rarer in software, but more common in hardware, WSS. That can be delivered by Maestro, Aztech and PCM20.
So big question: do you have two ISA slots?
If not, I'd say keep the current setup. Maestro 32/96 is excellent for SBPro2 and WSS plus bug-free MIDI. Oh, and the very nice Dream synth.
If you do have two ISA slots, you can have fun - AWE32 plus something with bug-free MIDI (and SBPro2 with correct stereo), which could be any of the other ISA cards. I'd probably choose the Maestro 32/96 because of its Dream wavetable.
And either way, add the PCI card of your choice for Win2k if you really want that.
You can easily have two cards active at once, just set to different resources. Generally it's the older games that prefer default SB settings and read the SET BLASTER variable, so I'd set the SBPro2-compatible card to A220 I5 D1 T4 P330 and the AWE32 to A240 I7 (or 3) D3 (or 0) H5 P300 E620 T6, and (manually) put the SBPro2 settings in the SET BLASTER variable. To choose the card, just enter the relevant settings in your games.
As for other options... if you really want one ISA/DOS card only, the only options with bug-free MIDI and decent SB16 support are Avance Logic ALS100 (non-plus) and C-Media CMI-8330. The ALS100 has the option of real (or more commonly: 100% clone) OPL3 as an advantage, but you correctly say that doesn't matter too much for late games. Bigger problem with both is that they are late, low-end chipsets generally implemented on cheap crap boards. There are some fairly decent ALS100 boards out there, but nothing that comes even close to the level of quality of a Terratec or MIro card, at best equalling Creative. So I'd recommend two ISA cards if at all possible.