GA-5AA is a nice board for late DOS.
Most important question is whether you want DOS only (no compromises) or also want to do Win9x (involves compromises)
If DOS only, accelerated features of hardware is generally not used, and compatibility is key.
My recommendations in that case:
- as fast a CPU as you can find, K6-2+ or K6-3+ are best, but K6-2 or K6-3 will be fine too.
- 16MB PC-100 SDRAM (the smallest DIMM you can find) - no DOS game needs more than this, and larger amounts of RAM can actually cause memory detection issues ("not enough memory" even though you have tens of MB to spare)
- S3 Virge GX(2) AGP card (cheap, extremely VESA compatible, good raw framebuffer performance). As always, cheap crappy S3 cards can have bad image quality, but something like a Diamond Stealth 3D 4000 would be great.
- sound cards are a huge rabbit hole, before looking for specific types, clarify what it is you are looking for. Do you want the same (probably objectively crappy) experience you had in the 1990s? Do you want 'wavetable' MIDI music? (and if so, 'period correct quality' or as good as can be bought?) Do you have a fetish for certain brands (Gravis? Creative? Audiotrix?) And how much money are you willing to spend? If you don't have a clue and want something cheap and easy, go for anything with an Aztech AZT2320 chip on it. It will give you near perfect SBPro2 compatibility, a real integrated Yamaha OPL3 and a bug-free MPU-401 MIDI interface you can use for wavetable stuff if desired. They also tend not to be very noisy. In any event you want an ISA card with hardware Soundblaster (Pro2) compatibility.
Now, if you also want to run Windows 9x, that can be done, but you need to compromise, as then accelerated functions become relevant.
- CPU same as above. Bear in mind that even the fastest K6-3+ will be slow for Windows 98 games (by the time Windows 98 was supplanted by Windows XP, it was Athlon/P4 era)
- At least 64MB of RAM. It's possible to limit the amount of RAM for DOS in CONFIG.SYS. Do so down to 16MB. Over 64MB, things get complicated and what is best depends on the revision of the Aladdin V chipset on your motherboard. If it's G-revision, you can add as much RAM as you want up to 512MB. If it's E-revision or earlier, only 64MB is cacheable by L2 cache and you're best off installing 64MB only, unless you have a K6-3, 2+ or 3+ with its own L2 cache on-chip. Then you can ignore that 64MB limit.
- in Windows, it's the graphics card that's the rabbit hole. Voodoo cards are great (and support good VESA for DOS too), but cost an arm and a leg. If a Voodoo3 is too expensive, look to nVidia, eg a TNT2, for good performance and still good DOS compatibility. Caveat here is that the ALi ALaddin V chipset was notorious for compatibility issues with nVidia cards. Most were fixed by combination of BIOS and drivers. Be sure to upgrade BIOS to latest version before you start, install ALi chipset drivers (AGP miniport!) before installing nVidia drivers, and be prepared to play with multiple driver versions before you get something stable. Note that you want as old nVidia drivers as possible (i.e. that support your chosen chip), as the overhead of later drivers is huge and this is a slow system. I would not recommend any GPU on this board as the AGP slot and VRMs probably can't deliver enough power for a big hot chip with T&L like the GeForce series.
- for unaccelerated Win9x stuff, the same ISA card as for DOS should be usable, particularly if the card supports WSS (as the AZT2320 does). For more interesting stuff, several chips have software wavetable synths in their drivers, such as the Yamaha YMF74x series. Also Aureal-based cards and Soundblaster Live cards offer positional audio, although I doubt a K6-2 will have enough oomph to run games that support that particularly well. One thing to remember is that you can have multiple sound cards in the same system, so it's perfectly acceptable to have an ISA card for DOS and a PCI card for Windows, for example. That reduces the compromises you need.
