Pairing of PreAMP and Amplifier

I have reached a fairly high level of audio in my home but I am unclear as to the importance and best "rules" of matching the pre amp and amplifier objectively. I currently am have Audio Research REF-6  pre amp and a new Burmester 911 MK3 solid state amp which I bought on a whim.( I previously had a VAC 300.1A which was a wonderful tube amp.) I was thinking that I should try an Audio Research REF160S- monblocks are a bit much for my room.
 I do enjoy buying and selling audio but I am also getting tired of all the stresses of same. I am trying hard to find the BEST combination and not sure if my current pairing is as good as I could appreciate.  I have recently acquired Avalon ISIS speakers...My source is CD - currently Audio Research CD9 but considering Esoteric.