Which/what type sub-bass (and surronds?) to go with SLX's and Denon 2807?

[bluesplayer]

Long winded background to get to question about a sub-bass and possible re-buy for surround speakers.

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I just got first HD TV a few weeks ago. My stereo is an old Pioneer system and it only supports Dolby Pro Logic. It does not have/support sub-bass speaker. It allows for only 2-channel, 3-ch (with center), 4-ch (front and rear surround reminds me of my Sansui QRX-7500 quad receiver which I miss!) and 5-channel surround.

Our house is small and the room in which my theater will be is small. Additional info - my wife is constantly rearranging things so permanent in-wall or ceiling surrounds are out of the question.

I will be upgrading receiver to a Denon 2807 (possibly 3806) in about a month. Even though they are 7.1 A/V receivers I will only be using 5.1 and the surrounds will be moved to the sides/rear when needed by hand.

Over Christmas without doing on-line reviews or forum visits I went out and listened to speakers. Again with limited space in mind I was looking at small or small profile speakers (I listened to Klipschs, Bose, etc.). I ended up with a pair of Synergy SLXs on Sanus stands for the prime front speakers. They had more depth/clarity to my ears then similarly sized/configured speakers (plus they look great as well as sounding well rounded good bass, nice highs and properly placed mids).

I also bought a Synergy C-1 center speaker. In the store it sounded great with the SLXs but at home the C-1 is a little overpowering of the SLXs (sound all seems to be focused in the C-1). It is quit possible that it is the old Pioneer amplifier and NOT the speaker Ill know more when I get a better receiver/amp.

Last week I was looking for SMALL bookshelf sized speakers that would sit UP FRONT with front speakers (on shelf) and would compliment the SLXs in pure stereo configuration but which would do double duty as surround speakers. After much listening I ended up with some Klipsch RSX-5s. They do SOUND GREAT as stereo speakers. I havent yet tried them as surrounds hopefully they will work well. The RSXs hit some of the highs the SLXs miss (and add some singer voice clarity to whole set-up) so the RSX and SLXs seem to mesh well.

Obviously this is a very mismatched system so questions are:

1. Im now looking into a sub-bass but it has to be a small sub-bass no wider than say 15 inches. I dont know if powered or un-powered is required. Im looking for good lows/bass [but not earthquake level rumble] that will complement the SLXs (with GOOD cross-over/separation between it and the SLXs).

2. I love the RSX-5s as stereo speakers but would something else (again they have to be small and movable) work better for surrounds?

Thanks for any help/suggestions

Larry