That's all you got for this guy Leafs? Why say anything at all? And have you heard of 2channel bypass ever? That might be something you could look into because I think it negates your comment. To answer your question, Blob7, you start by doin a little research and askin some questions. You can buy a whole lot of *great* sounding system for $50k, a whole lot.
I will at least try and point you in the direction I'd go if I had the dough. But first, there is a problem here. You don't say anything about video. Does that have to be squeezed into the budget too? If so, it could be tough. You could spend $50k in just the projection unit and a screen alone, not to mention video scalers and satellite receivers. It doesn't say anything about that, so I will assume you have that all figured out.
As far as electronics, I will just skim across some basics. To begin, I would suggest a Theta Casablanca II HT preamp/processor as the brains of the outfit. It does it all, sounds great and no one will laugh at you ever for having it. In addition, the thing can't be obsolete because of the way it's built; you can update the hardware and the software any time a new format comes down the pike. Proceed and Meridian make similar units that would also do the trick.
For power, get the amperage of your choice. Just about all the top amp manufacturers are making amps in multichannel configurations. Look at Ead, Proceed, Bryston, Theta, etc. there are a lot of others. Usually the maker will have a flagship 2ch. amp and also a 5 channel amp. The 2ch. runs the mains, the 5ch. for the surrounds. Proceed, for example, makes the HPA2 at 250 wpc, and the Amp5 at 125 wpc--there's your 7 channels. Bryston makes the 4Bst(2 ch.) and the 9Bst(5ch.) which are the same power output as the Proceed.
For speakers, I say go with Aerial Acoustics. They are among the best, and again, noone could ever laugh.
For digital, you got a decision to make. Try and go with an all in one DVD/CD player, or split the work and buy both a DVD and a CD player. I got the Camelot ($2500 used) that does double duty and am quite happy with it. The Camelot sounds great for both 2ch. and HT, has tons of gizmos on it, and comes in second only to the Ayre DVD player (loaded $12k). But if you bought the Ayre, you'd have to laugh at yourself to keep from crying--at least I would.
Don't forget cables, this will be a big part of the budget and if you skimp, you'll be sorry you did. You can get cables from many on line dealers--but it is a pain to figure out what you'll need and what quality is good enough.
There is a ton more that I am presently too tired to write about, maybe some other of our fine membership will pick up where I am admittedly slacking. Hope I've helped.
