How/where did you add that ASM file into computers bios? It doesn't makes any sense, you just break some BIOS checksum so it doesn't boot. The ASM file is just a text representation of sound chip configuration data and computer bios doesn't know about it/how to hadle it. The config data makes sense only for soundchip itself and you need to put it in separate I2C EEPROM connected to soundchip, nowhere else...

Yes, my ignorance can be as great as my determination to make things work, that's how I've learned most of the stuff...
I dumped the bios and opened with an hex editor to see the contents, and there was plenty of "blank" memory, and a big part that just had something like text saying ibmBios so I replaced that with those contents of the asm file...
I looked at the cs4237b datasheet, I wish I knew how to add in a breadboard the i2c eeprom and even the joyport and wavetable header if possible but can guess how much of a mess it Is 🙁
I think it was worth a try, that small computer is great, it's a shame they used that cs4235

Oh, this really had not chance to work...
If you want to add external I2C EEPROM (if not on the board), you just need to hook wires at pins:
14 - SCL - connect to pin 6 at EEPROM
8 - SDA - connect to pin 5 at EEPROM
A0, 1, 2 (pins 1,2,3) and WP (pin 7) at EEPROM connected to GND
SDA also needs pull-up resistor to +5V, something like 4k7, fot SCL pull-up is not needed (has internal)
You can solder tiny wires directly to EE chip, no PCB needed, just fix it somewhere with hot glue.
Then load config data via RESOURCE.EXE from DOS.

I didn't look at soundchip pinout if they are really pin2pin compatible. I expect you did (best to open 2 datasheets with pinouts side by side and check all).

yes, I did, the only notable differences where the need for filter capacitors on the cs4235 but shouldnt be so different. First I need to recover the original bios from the computer, had to unsolder the chip and installed it in a socket, but don't have a plcc eeprom burner, and I don't know if the backup I made with uniflash is ok, as it differs from the available "firmwares" for that thinclient.
I'll try to get that i2c eeprom 24c08 and solder it, it is interesting to see how the cs4235 was able to work without any eeprom and the cs4237 needs it.
thanks a lot for your help, I was just checking the datasheet and the diagram for the tinyllama, it just shows what you told me

The CS4237 doesn't absolutely need an EEPROM; there are other ways to make it work, and you seem to have been pretty close already. You already had the replacement chip soldered well enough that it could be identified. That doesn't mean that your soldering was perfect, and that may have been part of the problem. However, trying to insert the ASM file into the BIOS was a bad decision. Even if the firmware or BIOS-like code had the right routines, and you knew the correct location to place the Crystal data, the ASM file is not likely to be what you needed. Usually, the "compiled" hex representation is what is used.

If you get the machine running again, there are tools that may help, as well as a detailed discussion I had on the subject with Mu0n here. That would be a good place to start. Naturally, you can ignore all of the parts about programming the EEPROM, since you don't have one on the board, but the rest of the tools and discussion should help.

Ok, while i'm still waiting to recover that thinclient in lack of a proper bios dump... I decided to do the same procedure in a crystal cx4235 card I got recently, just to see if it works... Couldn't find if there is any difference between cs4235 and cx4235 but tried anyways, so replaced the chip and ran pnp36.bat included in a driver package to rewrite the contents of the eeprom. So.. success! It works perfectly fine... now the only problem is I'd like to add to the card a waveblaster header... but that will be some other day.
I added the 24c16 eeprom dump before and after flashing just to have a backup... before flashing the card was detected as an unknown csc4625 by unisound...
By the way... I remembered the cs4235 was awful when playing fm music in some games... with strange sounds and missing notes, but could it be possible that in this card or by being the cx4235 was a bit better? it almost felt like sounded ok..
anyways I had the cs4237 and wanted to do the upgrade.

Well, good to know the direct replacement works. You probably had some soldering problem before...