I've never used SPDIF before, so I can't comment on that, but I think that an audio interface might be an option for you if SPDIF doesn't work out. There are a ton of audio interfaces available that connect through USB or FireWire. Because these were intended for recording music, they have very low latency, so they will require more resources from your CPU compared to regular sound devices. I've used mine for gaming before and didn't notice any major performance costs, but that's also on my desktop, so your mileage may vary. A decent audio interface would have good DACs and audio circuitry in it which might address your problem, but I'm not sure about SPDIF. There does seem to be a few available with SPDIF (https://www.audiosciencereview.com/forum/inde … pdif-out.50870/), but they will probably cost a lot more than your adapter.

If you are getting hum, you might have a ground loop problem. You might be able to fix it with a cheap ground loop isolator. I had terrible hum with a COVOX/DSS replica that I bought, but a $10 isolator fixed the problem for me.

You could try the Behringer UCA 222 or 202 which is a pretty cheap and basic USB audio interface with fairly good sound and SPDIF output, although I'm afraid the drivers might not work under Windows 98 - the oldest supported OS is Windows 2000 according to the manual.

Any dirt-cheap USB audio device should work fine with windows 98, at least for basic stereo output. Multichannel will likely need win98 second edition.
If you're aiming for SPDIF output don't bother spending significant amounts of money; it's very simple to pump digital audio from USB to another digital interface and since it's digital there's no processing involved, paying extra money for "superior" quality is a complete waste. Also don't bother with anything that isn't "standard" USB audio.

The builtin soundcard in the machine would be irrelevant and unused when a USB audio device is used for output.

I'm sort of leaning toward firewire to not lose a USB port plus its in a more convenient place than the USB ports for where I'm planning to use it (not on my lap 🤣), but these seem way pricier than the USB ones, I guess because they're older/rarer by this point.

It doesn't have to be SPDIF, just digital/lossless, not sure what other connectors were available at the time.

Also not sure what the speed of the FW port is, its the smaller version of it though.

SPDIF is more or less the only transport format for lossless, it was the defacto digital interface (using either RCA/coax connectors or TOSLINK/optical).
It's going to be a lot easier to do with a USB adapter, due to being a well defined standard with built-in support included in the OS - you can take any standard USB audio device made today and it should work with win98.

You used to be able to get dirt-cheap usb audio breakout boxes like this for only around $10, I don't really know why the price has gone up over the years. Their analog outputs are pretty bad (poor quality DACs) but the SPDIF in/out worked fine, and having them connected via a cable was more convenient than having a device directly connected to the USB port.

+1 for grabbing an (ideally period correct, for the drivers) USB audio interface. I have an M-Audio Transit (this one, not the newer Pro) for use with classic Mac OS, but it should work for your use case too - has 98SE drivers and optical SPDIF. Unfortunately there's none on eBay right now, but keep an eye out. Mine was around ten bucks.

elszgensa wrote on 2024-04-05, 23:54:

+1 for grabbing an (ideally period correct, for the drivers) USB audio interface. I have an M-Audio Transit (this one, not the newer Pro) for use with classic Mac OS, but it should work for your use case too - has 98SE drivers and optical SPDIF. Unfortunately there's none on eBay right now, but keep an eye out. Mine was around ten bucks.

Thanks

I forgot it also has one of those PCMCIA slots and there seems to be a ton of options with this too PCMCIA Sound Cards