Don't mean to raise this from the dead too much, but I have this specific ET4000AX Speedstar card. Acquired it a few weeks ago at the recent VCFed swapmeet in NJ, sitting in a 386DX build that was pretty worse for wear, however this was the crown jewel that made me go for it. There doesn't seem to be much in the way of documentation for this specific kind of card, so I'm dropping it in here as this is where the party is (was!) at for ROM dumps of these very nifty cards.
it has BIOS 4.23 on it and the Music TR9C1710 DAC. Based on the latest datecodes on the board I can only assume this card was from early, early 1992. from what little I can gather about this particular card, this is the precursor to the Speedstar24, but if you waited a bit, you could upgrade it to a Speedstar24 with an upgraded ROM set and DAC... at least, that's what I've read from one of the sources I was able to dig up. I'm not sure what the extra mask ROM there is for, however. character set? I can't figure out which mask ROM type it really is to get my T48 to read it. I did dump the ROMs for the card otherwise, although I don't know if it matters much... I think this is a common ROM set.
Given I have recently bought a UV-C EPROM eraser, I'm going to try and upgrade the BIOS on this card to one of the later 5.x/6.x ROMs and see how that goes. Mine has an issue where higher resolutions than 640x480 are rather noisy, so I want to see if that helps any before I bite the bullet and throw money at the problem for another DAC. Mind you the highest res it'll likely ever see is going to possibly be 800x600@8bit under WFW311. 640x480@8bit is pretty much perfectly fine.
I also have a Weitek 8256 card here with a Sierra SC11483CV on it I could always yank off and drop in the socket, seeing as that seems to be another compatible DAC, albeit only a bit better than the one I'm working with now.
Currently this card is sitting in my PS/2 40SX, and was a much easier upgrade than yanking the motherboard and installing the extra ZIP-40 RAM for the onboard video... but I did need to upgrade the machine's BIOS before it would properly enumerate at boot. Doing this on the earlier March/April 1991 BIOS compared to the September 1991 BIOS is futile.