As for the preamp question, I think it's determined by how much you value convenience and how you use the system. A separate 2ch pre would allow continued flexibility of upgrades and, possibly, better performance on music reproduction. It also means more cables, more switching, etc. - if you have others in a family that are using the system, you'll probably get more complaints. I also don't think you're going to be able to avoid future upgrades regardless of which way you go - pre/pro's will continue to evolve rapidly for years to come, as I see it, so regardless of whether you buy today, tomorrow or in a couple years, there will always be a compelling reason to wait.
My advice, which I have followed myself in this fabulous pursuit, is to buy the best pre/pro you can justify knowing you'll want something better in 3-5 years and research the purchase with an eye on 2-channel performance (analog pass-thru, etc.) I think this approach maximizes performance for $$$ spent. -Kirk