So I thought I would throw in my new found experience into the mix.
I recently got rid of the RER for an aftermarket unit. I originally had the RER sub output tapped into and was using that to send signal to my Audison 5.1k amp (only the sub was hooked up then). The sub was deafening! Pre stealthbox/Audison 5.1k, I would listen to the RER at a vol of 26 with the windows down and could barely hear/feel the sub. After stealthbox/Audison 5.1k, the bass hit was awesome at low volumes... and with the windows down I couldn't go past 20 without the bass drowning all the mids/highs. So when we installed the aftermarket unit, we decided to run RCAs to the Audison 5.1k and rewire the entire system (including the sub). We pulled full frequency from the driver door and, while it does sound amazing, I don't get deep bass again until I am in the +20s. With volumes that high, I can't hear my GT Haus opened at 5000 RPMs w/ the windows down!!!! I can tell you that the HK system REALLY wakes up with more power and seems to be handling it well.