As per replies in your other thread, you do NOT need a pre amp to run an electric guitar or bass guitar into your mixer.
Pre amps, as the name implies, amplify your signal. Instrument signals are actually already louder than a microphone (so it doesn't need a mic pre amp) but lower level than most line inputs (so going into those doesn't work well either). Also, the impedance is much higher than most mic/line stuff and, for the right frequency response, you need to sort that out as well.
The magic box that does all this is called a "DI" (Direct Injection) box. It knocks down the level and converts to XLR to go into the mic input on your mixer. Even cheap passive DIs (effectively just a transformer in a box) can sound good. In your other topic, Arcaxis suggested the Behringer DI2 and this could be a good choice but there are lots of others.
The so-called Tube Pre Amp in this thread is a gimmick that you don't need and that won't do much good to your sound.
However, like others, I also suggest that you don't discount a USB interface. If (as you imply) you're running your mixer into your computer via the built in sound card, this is guaranteed to make a mess of your recordings. The built in sound cards these days tend to be a single 39 cent chip on the motherboard and, in terms of noise and headroom, are made for Skype calls, not music.
Lots of USB interfaces still have drivers that run on XP...one I know I can recommend is the Alesis iO2 which has instrument inputs, line and mic inputs, direct monitoring and MIDI. It's also dirt cheap these days. You could use it to run your bass straight into your computer, or (with the line setting) you could run your mixer in.
I strongly suggest you either go for a USB interface or a DI box and stop looking at cheap entry level pre amps that are a waste of time for what you want to do.