Why Rumble One Side of Album

My KAB RF1 arrived today.  I recently bought a Boz Scaggs Greatest Hits Live record that made my woofers look like they were going to jump out of their enclosures.  With the RF1 there was NO woofer pumping whatsoever. 

The clipping indicators on my amps often flash (I think they are overly sensitive!) when I play vinyl.  I turned it up louder than I usually listen and they did not come on at all, so it appears to have lightened the load on my amps also. 

I only listened for a few minutes (work and all that) but didn't notice any degradation of sound.  I'll be able to do some extended listening later this week.

@mijostyn the RF1 is supposed to cut at 20hz. I haven't listened to anything bass heavy yet. First impressions are very positive. Bass seems present and tight, nothing noticeable affecting upper frequencies. 

@mijostyn The jury is out on the Kab filter at this point.  As you mention, I don't feel the energy of the subwoofer quite as much, but so far everything sounds "better".  It will take some extended listening to sort it out and if I don't like the Kab unit, it was less than $200, one of the least expensive items in my analog chain.  I have 4 subwoofers with a combination of 4 15" drivers and 2 13.5" drivers, so I'm not lacking for bass, but there is a noticeable difference.

@mijostyn  The dual 15" subs are Rythmik F25. The two 13.5" are SVS SB13 Ultra.  I'm really happy with my current preamp, the Herron VTSP-360.