My advice is to not go nuts on the hardware and buy the latest and greatest - it'll be a waste of money. A modest system will be more than enough for an LMCE core/hybrid. My core is built using the cheapest dual-core AMD CPU I could find (AM3), and has a mere 2 gigs of RAM. This is plenty. I might add some RAM if I get any spare, but I'm certainly not going to rush out and buy it.
Motherboards are generally OK, but there are one or two that might give you problems, depends what you are using it for. If you want to be certain, check out the user setups or the mainboard category on the wiki.
There is a very good TV capture card page on the wiki also.
I never bother with sound cards, onboard is always good enough for me.
IR devices? Surely you would already have these... unless you're talking about controlling them, in which case search wiki for USB-UIRT and think about getting some extenders for it for added reliability.
Remote controls - loads of options here. Personally I prefer a combination of mini keyboard/mouse (check out the Rii mini keyboard, it's wicked) for use with onscreen orbiters, and also mobile orbiters in the form of a 7" Internet tablet. There are many IR remotes and gyro mice and various other things that will work also.
Final tip; not sure what your Linux experience is, but my advice would be to take it slowly. Just get the hardware for a basic core/hybrid, maybe a TV card as well, get that running, and have a play. Then maybe get a single MD, see how it all knits together, and add the really cool stuff later.