A Vortex 2 is a Vortex 2, as far as sound quality and 3D performance go. The Revision B chip is a tad faster, but sounds no better. Not that it needs to sound much better - A3D 2.0 is superb in most of the many games that support it. Sounds really do seem to come from distinct, 3-D locations, especially when you're using headphones.
All of the non-3D sound capabilities of the SQ2500 are well up to scratch, too; its inputs and outputs are very low noise, its recording quality is superb, and of course its digital S/PDIF output, being digital, is noise-free.
The very low noise design makes the SQ2500 perfectly suitable for studio work, provided of course that you can make do with just one external input jack. Make up cables for the internal CD and AUX IN jacks as well, though, and you could use a standard Vortex 2 card as a three channel stereo mixer without much trouble.
The SQ2500's MIDI output has an outrageous number of possible simultaneous voices (64 hardware, up to 512 more with software mixing), but the standard 4Mb instrument set is merely OK. It sounds acceptable, especially with the two simultaneous configurable effects you can layer on top of the music. But if you want something better, a whole different instrument set is only a download away - compatible DLS 1.0 sample sets can be had from various sites, like this one.