If your source lacks of gain and suffers from poor signal to noise ratio, the best you can do is not add even more noise.

Since you aren’t going to invest in high-end mixing desks that offer lots of gain, the next best thing is to use your device with a DI and a clean, solid state microphone preamp.

I would advise you NOT to waste your money on cheap small mixers. Save a little bit more and get a couple of high end DI like the Countryman Model 85 and a decent and clean preamp. Then you can get the gain you want and not introduce more noise to your (already) noisy device.

Eitan