I would recomend looking at the BASS knobs for Taramps, I think the one that works as an antenuator ( and as a bonus also acts to EQ the frequency bands) is around $55, not cheap but well worth it. The cheep one is an 2 channel inline RCA type, not a remote (phone cable) type. It is, if I recall, simply a volume control.Taramps is legit, Make the power they claim and are damn cheap. They do not have a bass knob included I believe but one can be purchased for a little $.
I hear the adjustment knobs on amp (gain, low pass) are a little cheap.