Fishing for Speakers with Krell HTS5.1 &Showcase 5

I bought a Krell HTS 5.1 and Showcase 5 amp off of Audiogon. It is a great combination. I would highly recommend them. The quality of the sound is spectacular. I have pretty high-end tubes for my 2 channel and the Krell is along the same lines in quality. I am currently using B&W speakers. I tested some 600-series in the front and rear. The Krell was much better than the 600s. I noticed right way with the 600s that there was not any top air. I want something better but only for home theater. I have a tube 2-channel in a different room for stereo. I am currently using a B&W CMDNT1 center with McIntosh ML1 which I bought new in ’73. I am using B&W LCR6 S2 in the rear. The 600s are definitely going. The CMDNT1 is not bad. It could use a little fuller sound. The McIntosh I have had a long time but they have a nice tone. I am still fishing for speakers. I thought about Revel M20 but I don't know if I would like the center channel. What speaker would you use for home theater only? With home theater only is there any reason to run large speakers in the front L & R? I have the large HSU sub which will rattle my windows currently. My room size is a rectangle 23x17x9 with acoustic tile on the ceiling and wood floors and walls. The room has nice sound but can’t tolerate a lot of bass.
linn 5140
There is one more issue with my room. The back speakers need to set on a builtin cabinet. There is not really room for floor standing speakers in the rear. Also I am looking for a good full sounding center speaker which can set on top of a very large rear projection HDTV to go with the rest of the speakers. What combination of speakers would you use?