A month late but here is some info. The main point is that I see no evidence for this chipset to be compatible with the gravis ultrasound.

http://benlawrence.com/nt150/faq/faq_2.html

Not mentioned on the site anymore, though by a search on Google, they appeared to at one time have a page describing the compone […]
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Not mentioned on the site anymore, though by a search on Google, they appeared to at one time have a page describing the component. Further hunting on the site seemed to indicate that the CS4235 is a pin-for-pin compatible replacement for the CS423x series. Its specs are as follows:

Product Description

The CS4235 is a single-chip Computer Audio system that is pin-compatible to the CS423xB for many designs. The product includes an integrated FM synthesizer and plug-and-play interface. In addition, the CS4235 includes hardware master volume control pins as well as extensive power management and 3D sound technology. The CS4235 is compatible with the Microsoft Windows Sound System standard and runs software written to the Sound Blaster and Sound Blaster Pro interfaces. The CS4235 is fully compliant with Microsoft's PC 97 and PC 98 audio requirements.

Product Features

Compatible with Sound Blaster®, Sound Blaster Pro®, and Windows Sound System®
Advanced MPC3-compliant input and output mixer
Enhanced stereo full-duplex operation
Dual type-F DMA support
Integrated Crystal® 3D stereo enhancement
Industry-leading DS data converters
(86 dB FS A)
Internal default plug-and-play resources
CS9236 wavetable interface
CS4236B/CS4237B/CS4238B register-compatible

Actually, I ran across a discussion pointing out that cards with a cs4231 compatible DAC(cs4235 probably falls into this category) will function as the DAC of a GUSMAX by setting MAX's ultra16 envirionment variable with the cs423x settings. I have a GUS and some cs423x cards but I havn't tried it out yet; on my todo list.

Thanks for pointing that out. Such undocumented compatibility might come in handy (Getting 16-bit digital sound over sbpro-8-bit when WSS is not an option?). I have a cs4232 card myself but I haven't got it installed currently.

Yes, alternatively you can configure as WSS, as the cs4231 was the DAC of the WSS 2.0, and backwards compatible with the DAC in WSS 1.0(AD1848.)

Note that the MAX's DAC was hardcoded to follow the base address of the GUS; 2x0 gus addr = 3xc max dac addr, and 3xc isn't a wss addr and all of the generic cs423x based cards I've seen use the standard wss base address selections, so if a program works off of the hardcoded assumption rather than the envirionment variable, the trick won't work for that app.