new HT receiver or preamp

currently using a Marantz SR6005 as the pre and for side/ rear power in my HT system ( using it to power the sides and rears of my 7.2 system). I'm deliberating on do I replace it with another receiver, or go to a pure preamp. If I go with a pre, I could use some advice on which one.... If it helps, I'm using KEF Reference 5 speakers for the fronts and a 4C for the center. And a Krell S1500 to bi-amp all three. Have a Sunfire 5 x 200 that I can use for the sides and rears if I go pre... your thoughts would be appreciated. Marantz? Emotiva? Macintosh?  Open to suggestions in the < $5000k ish  level.  

Really like the Marantz. Not impressed with the Emotiva HT pre I heard, but that could have been the weird system I heard it in ( could have been the owners fault lol  sad but true) . 
I would get a used Marantz AV8802A processor.  Then maybe look for something like a Parasound A31 3-channel amp to power your fronts.  Use the Krell S-1500 for side/rear.  I don't really think you will get much from bi-amping the KEF speakers.  I think it's better to get a really hefty high current amplifier. 
understand your point.... I've tried both....I can tell you for a fact that they really sing bi-amped ...  To my liking/ ear they are more dynamic and image even better (which is saying something) . Horns are really incredible    FYI, I am using my subs set at 60htz even in stereo  (sound is better at 60 vs 80 in my application)  JMHO YRMV