Which one defines sound: Pre amp or Power amp?

Since nobody has responded to your question yet, I might as well bite.

Before I give my opinion, I would like to highlight that both your options of adding the McIntosh to your existing setup are not too feasible as your other stuff(especially the Energy speakers) are mainly for HT. If you are considering the Mcintosh pieces, you might as well revamp your whole system by getting both preamp and power amp and changing the speakers as well. Then only the full potential of the 2-channel setup can be realized.

If you really insist, I would go with the preamp first, that if your speakers are capable of revealing the finer nuances and detail from the upgrade.

Leaving the Rotel in play greatly diminishes any significant upgrade in the system's performance.

I agree with Ryder. I would upgrade the speakers first, then preamp. I have McIntosh C42 preamp and MC252 amp. Without speakers that can extract the full potential of the McIntosh pieces, I wouldn't bother upgrading to better pieces like McIntosh, Classe, Pass, C-J, etc.

IMHO, speakers diverge from neutrality more than any other component. That said, this divergance is generally in frequency response, clarity, and distortions that are consonant (harmonically related) with the input signal.

Electronic components, while having lower levels of distortion, have distortions that are "electronic" sounding, and this is usually much more problematic than the distortions of loudspeakers, so I think that you are barking up the right tree.........kind of. Better speakers are just going to let you hear the distortions of your electronics that much more clearly. A bad thing.

Again, I really don't see putting Pirellis on a Yugo and would question the logic of teaming up either of the existing components with a very high end piece. You are just not going to get the bang for the buck, unless you will buy, say the 252 and be able to buy the 2200 in a few months, and then it won't matter; buy whatever you can get the best deal on now.

If you like the Mac sound and reputation for reliability as well as the domestic connection, why not buy one of the excellent Mac integrateds, now? Be done with it, the cost is not going to be that different to get a 6300 or 6500 and the whole electronics issue is dealt with and you can begin saving for that, much needed, loudspeaker upgrade. Just my 2 cents.