Almost all mixers will use 6.3mm inputs although some also use RCA. One way or another you'll likely need adapters to convert to 3.5mm TRS.

Instead of a mixer, you could consider a passive A/V switch. Most A/V switches use RCA connectors for audio, so you'd need a couple RCA-to-3.5mm adapters. This is probably the least expensive option.

Alternatively, if you want a mixer specifically I'd take a look at the Edirol M-10MX mixer. It's compact, has 10 channels (5x stereo) and is powered. It's more than what you need, but it will do the job. It has a mix of inputs including RCA, 6.3mm and one stereo 3.5mm input. You'll likely need at least some adapters to hook everything up.

I usually hook the output of one into the input of the other and have both on.

fractal5 wrote on 2023-08-05, 18:05:

I have two computers with audio cards, these are regular PCI audio cards, one for a DOS era computer, one for a Windows 98 era c […]
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I have two computers with audio cards, these are regular PCI audio cards, one for a DOS era computer, one for a Windows 98 era computer. I'd like to connect both of them to the same pair of speakers.

Everything is 3.5 mm TRS.

I've tried with a passive "dumb" mixer (which isn't really a mixer) that just connects everything together in parallel. My Sblive! (in the win98 computer) can handle this just fine, however, the AWE32 in the DOS computer becomes so low in volume that I can hardly hear it. I need to turn the volume way up, and that introduces a lot of noise in the speakers.

This isn't a good setup. So I think I need an active mixer with a built in amplifier so I can individually control the amplification on each signal that goes in.

Basically I need a "3.5mm TRS Audio Splitter/Mixer" from what I understand.

Seems most of these are meant for 3.5 mm TRS input, but provide 6.3 mm unbal output. I need 3.5 mm output.

Any recommendations?

Should I just get one that does 6.3 mm output and use a converter?

I think you indeed need an active (powered) mixer and adjust your input levels accordingly so they all output at a similar volume when reaching your speaker. Passive (unpowered) mixers can be used as an expansion to the active one in case you need to connect more inputs than your active mixer supports.

PS: To keep things simple, you can use a passive mixer that can adjust input levels, and connect a simple headphone amplifier between the mixer's output and your speaker.

Conversion between different form factors (3.5mm, RCA, 6.3mm or even XLR) can be done through cables or adapters, though be wary some conversion may weaken the signal output requiring you to amp it on the other end to equal out.

I'm using this little passive mixer from Ali. Works good for me.
https://m.aliexpress.us/h5/item/2255800342830911.html

Search for audio switches. I use this one: https://nedis.com/en-us/product/computer/cabl … mm-female-ivory
plugging it in in reverse (2 PC to 1 speaker set instead of 2 speaker sets to 1 PC).

Works fine.

Zerthimon wrote on 2023-08-06, 13:37:

I'm using this little passive mixer from Ali. Works good for me.
https://m.aliexpress.us/h5/item/2255800342830911.html

I second that. I have it connected to 4 input sources: 2 modern PCs, one Pentium MMX, and one MSX! Everything works fine. You adjust the levers once to equalize all inputs then you forget about it.

I got a Behringer MICROMIX MX400.

It works, but I find that the AWE32 is very muted, still. I have to turn the amplification way up on the channel the AWE32 is connected to. My Windows 98 machine (Sblive!) doesn't have this issue.

Perhaps the AWE32 has some old capacitors in need of replacement, or is this something I can adjust in driver settings? config.sys, autoexec.bat?