Have a pair of REL S3 HO and they don't produce enough bass

Hi all-

Just picked up a pair of REL S3 HO subs to work with both my 2 channel system and my home theater. The high output speaker connections on the subs go to my 2 channel system and plug into each mono block amp. The LFE connection from each sub hooks into my Anthem 720 receiver for home theater. 

For the 2 channel system it seems to work well. Nice low bass helping out my Focal Kanta No. 2 speakers. 

However, for the home theater system, they just don't produce enough bass. I have to turn them ALL the way up using the sub's LFE volume control, AND turn them all the way up in my Anthem receiver settings to get any semblance of home theater bass. I know this isn't normal, so something has to be either wrong, or the subs just aren't meant for home theater use.

I was using a pair of SVS 12" subs and man those things rocked. However, I picked up the RELs so I could integrate them with my 2 channel system as well, something the SVS' could not do.

Any idea what could be the problem? 

A side note: I have NOT run Anthem's ARC program again since buying the RELs. Perhaps that could be the issue, but I didn't think it would make that much of a difference. However, I could obviously be wrong. :-)

Thanks!