Adding Sub to current system

No problem integrating one of the upper end REL subwoofers into your system. Once you do you will realize you are missing a lot.

One last point, my $ for a sub is limited to around $750, hoping to find something on Audiogon, am I wasting my time?

Rpg - If you go with Rel, depending upon which model you prefer, you might have to stretch your budget a bit. I can tell you that my Rel R-305 is a fantastic match for my Sonus Faber Guarneri Mementos. Someone has an R-305 for sale right now on the 'Gon and the asking price is ~ $150 above your approximate budget limit. I do not know the seller nor do I have any connection to the item for sale.

I have recently experimented with bringing my sub from a dedicated home threater into my two channel system (consisting of paradigm signature 2's). I immediately loved the additional bottom end as the sub really filled out the presentation and created a much more enveloping sound. However, I still don't feel that I've got the placement, crossover, and phase perfect. Honestly i don't know if I ever will. Rather that spending the bucks on a sub more suited to music and my monitors(was thinking about the paradigm sub 1 but that a big chunk of change) and trying to get it perfectly integrated, I'm now just going to upgrade to a floorstanding speaker that can play close to full range.
SB

Hi Rpg,
it might sound silly, but I look at Craigslist everyday. Occasionally I see some incredible buys. Also,
HSU has some very decent woofers. One brand new 15 that will cost around $1000.00 delivered. The Rel's are really quite good, but I'm a believer that with some trial and error that you will get a good experience with several different woofers if you do your homework and take your time with setup.