What about the ALS100? According to rumors, this card is SB16 compatible. Did you try it in your rig?
Not all Vibra16 cards are that bad. The common thing with Vibra cards is that they have a different mixer (no bass/treble/in-/output gain sliders) and integrated OPL3 synthesis (no "real" OPL3 chip onboard).
The quality depends on the chipset; I have two very different Vibra cards here:
CT4170 Sound Blaster 16 WavEffects
Based on the Vibra 16XV chipset, this card is a nightmare. It can't take 16Bit DMA channels because it's missing the required traces at the connector. Line-out can be amplified, but it sounds dull either way. There is no wavetable connector or onboard wavetable, the name "WavEffects" is a bad joke. This card seems to come straight out of Creative's marketing hell, stay away from it!
CT2970 Sound Blaster Vibra 16 PnP
This one has the Vibra 16C chipset, and is actually a decent card. The only drawback is the v4.13 DSP, it will suffer from the "hanging notes" problem if you connect a General MIDI daughterboard. The line output is very clean, much better than on older SB16 models. If you are not going to use the MIDI port, this is a recommended card.