Can anyone hear the difference when you add REL subwoofers when playing two channel

Rythmik has high level connections, though. You don't have to use their internal high-pass filter. You can connect them exactly like the RELs (sans speakon connection, just use bananas)

Thanks dave_b2 and big_greg.

I think you both hit the nail on the head.  I might listen to the REL's one more time before making my decision.  Everyone who I have talked to says the REL subwoofers are very musical.  The biggest fear I have is the Rythmik might be too bassy.  It was encouraging to hear the F12 Rythmik's sound good and not boomy.

I wonder how the REL T/9i's perform with home theater.  However, I don't need to hear the windows in my house break to hear sound affects.  My primary reason for adding subwoofers is to hear more of what was recorded.  The one song that stands out is MIchael Wollney's song Little Person.  The first time I heard it I was blown away by the long extended bass in the background.  It just seemed to drop through the floor.  I just need to be careful that will not break up the floor and sound artificial.

I really appreciate everyone's responses.  You are all so helpful and knowledgeable.  Wow.......there is so much to learn as a beginner.  I have already made some mistakes starting out.  It started by wanting to turning our museum, the living room, into a room we would use more than twice a year.  I thought it would be nice to turn it into a room where we could hear music and HT.  We already have a surround sound system in the family room.  However, the family room layout can only allow for the TV to be placed in the corner.  There is not room to position left and right front speakers on either side of the TV, so I needed to put them on the adjacent wall to the right of the TV.  The living room is configured much better to set up the speakers in the right place to image better.  When deciding to turn our living room into a music room/home theater, I wanted to find either a receiver or amplifier that could do both 2 channel and HT.  I didn't know how to have a true 2 channel amplifier and surround sound system to easily switch back and forth easily.  A true 2 channel amplifier was no doubt the best choice for 2 channel.  I listened to a lot of tower speakers before buying my Paradigm Prestige 85F towers.  I liked the sound, but after my friend sent me an article discussing how a 3 way speaker design is better than a 3 way, I felt I made a big mistake by buying the speakers I did.  The Martin Logan Motion 60's ribbon tweeters sounded too harsh and the Bowers & Wilkins 804's lacked bass extension.  So did the Focal Aria's.  I wanted to buy speakers that were known to be recognized in the audiophile world.  However, what speakers are audiophile and what speakers are junk.

The one thing I have discovered in this group is everyone is searching for the perfect sound they can afford.  However, I am learning by the time you add an expensive DAC, an expensive turn table, speaker cable, you have dropped a lot of cash.  All this is fine if you have a wife that allows you to spend the money and who is passionate about music.

I wish I had joined this group before I jumped in because I think you all would have pointed me in the right direction to avoid the mistakes.

Thanks to all.  You are all so generous with your time to share your knowledge.

Although, I do like the idea of off-loading woofer duty from the mains amp (up to 80Hz). Currently I am looking for a cheap but great high pass filter - so far, a couple folks have told me to buy a resistor and a capacitor to build one myself, DIY style, but I might prefer an already made solution. If anyone has any ideas please let me know...

Absolutely an improvement from my experience if done right. 

I don't think you have anything to worry about as far as the Rythmik being "too bassy".  It's only going to sound that way if you have the volume and crossover set too high.  I would consider the F12 as an entry level sub.  You may find down the road you want to add another one (or 2 or 3) or step up to something with more output, depending on the size of your room, how well it integrates, and how much bass you want.