I installed the RF kit totally as they showed on the install videos.
You can tune the fronts and rears separately via the amp, not the HU.
The Hertz speakers do offer some more bass IMHO.

I adjusted my speaker outputs to 20/21 volts with a 1Khz tone with HU volume at 75% max & tone controls at mid. This worked perfectly after trying many other tuning methods. Seems at this volume level, the HD HU does not clip with any of the frequencies I put through it so that was a good volume to tune at. I maybe go past 1 notch halfway to get more than enough volume. As my daughter said - can't even hear us talking to each other cuz it is so loud at that volume. I have a stage III perf kit with rineharts exhaust and my audio is louder than my exhaust. People in my hood have given me dirty looks and hand gestures to turn it down while riding through (I wasn't trying to be obnoxious, was testing the audio).

I will add though, the music source does make a difference. Siruis station 52 (the music type daughter likes) is a good test for music. Clear Skrillex bass thumping etc. type music. Sometimes the old music is not the best source and doesn't sound so great - but once you get a well recorded/mixed sound source, the system wakes up and wakes everyone else up too.