Okay, and here's my advice:
The Cheap and Easy:
If you have a PIII and mobo for it, just take it. Don't care about via or intel chipsets, just avoid to install a lot of programs you rarely used in 1999 and will never need in 2010.
If you still have a Vooddo 3 - just try, together with a p3 500mhz this card will give you a great Unreal experience! All other games should work as well. And - as Tetrium mentioned - if you never had a top notch soundcard an Ensoniq Audio PCI aka Soundblaster 64 / 128 PCI will do the job just fine, and you will also have the dos compatibility you need for playing doom.
The Luxury (mad) variant:
Be patient and wait until you can get a Voodoo 5 for - let's say - less than 25$. If you have a highly paid job this will of course cost your company a lot more than 25$ because of all the time you spend infront of your screen, searching for the voodoo (during your work) and getting it for a low price. But as you're allready a retro maniac, who cares? Nothing beats shooting a voodoo5 for less than 25$. I got mine for €2.72.
When you have it you need a Vortex2 based soundcard together with a Soundblaster Live Platinum and a board that supports a P3 1Ghz (there are faster ones, but I understand that you want to stay in the "90s"). One ISA slot is obligatory and you will plug in a Terratec Maestro 32/96 with a Roland SCB-55 wavetable board attached.
The Exotic (and not so expensive) way:
Your first idea with the voodoo SLI wasn't so bad. If you have allready one voodoo2 8mb, getting a second with 8mb should be easy. With this combination you should be able to play Unreal in 1024x768. The advantage over the V3 is the fact that you will also be able to play older glide glames designed for the original Voodoo graphics (voodoo1) that with some tinkering will run with a V2 but never with a V3.
As host card the Matrox G400 isn't bad, because of the very good image quality. If it has a DVI output you can connect the adapter directly to the voodo2, avoiding a loss in image quality.
A Savage 4 based card would be an alternative, as you should be able to use the S3Metal api in Unreal.
If you have a board with a P3 1 Ghz dosbox will become an option, and a Yamaha YMF-724 based pci soundcard interesting. With the passthrough patch you will have a real OPL in dosbox and not-so-bad GM support. And you will have directsound3d, A3d 1.0 and Sensaura as apis in Windows. The Yamaha YMF724 has also limited dos support, but for all needs an ISA card will come in handy. If it passes your ways, a Turtle Beach Tropez or an Ensonq Soundscape 2000 (an OEM version was part of many gateway computers) will be a nice addition.