Which subwoofer to mate with my system...........

I have a full Paradigm Signature S1, C1, ADP1 system in piano black. I have a M&K MX-350 MKII in real cherry wood. The sub plays well but I need something that will plummage deeper and blend better with my SIGS......I am looking into a JL Audio F113 in piano black......Any Suggestions...

I would get the Paradigm signature sub(s).
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The "blend better with my SIGS" issue is a matter of setup. So changing subs will not solve that problem. It's true the M&K will not play as cleanly loud or low as some subs on the market today.

M&K 350
Paradigm Sig Servo
SVS PB13-Ultra
JL Audio F113

Considering the cost, the SVS is an amazing value. It was reviewed in the last Stereophile.

To address the blending issue pay more attention to setup (level matching in particular), consider a Velodyne sub (say a DD-15), use a Velodyne SMS-1, or use an AV receiver with good room correction.
Actually I use and SVS PC Ultra with a Velodyne SMS-1 and it integrates almost perfectly with my Maggie 3.6R's.