That's funny you bring this up. I had the other version that didn't work for me. Maybe this one could do the trick.

This is the one I had

Fosi Audio TDA7498E 2 Channel... https://www.amazon.com/dp/B077GWVHHN?ref=ppx_pop_mob_ap_share

Yes, you can use equalizer on PC and should be good enough. Somehow you got the car amp to work so it means you added a power supply, it's possible the sound is degraded because of the power supply it's also possible it's just fine as is.

If you can order from Amazon and return something if you don't like it why don't you try something like this?

https://www.amazon.com/gp/product/B077GWVHHN/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=basheaspe02-20&creative=9325&linkCode=as2&creativeASIN=B077GWVHHN&linkId=582e8e8f90cd5177c6f828726355abd7

Should have plenty of power to drive your speakers and then you can do a A/B test to see how the car amp stacks up.

A preamp has two basic purposes: 1) Volume control 2) Input switcher

How many inputs do you have? If you are just playing audio from a computer then don't bother with a preamp, use the volume control on the amps.