iMac as htpc (client)? realizable?

[Pharao2k]

Hi,
At First, Sorry for my "school" English, dunno how much of this is understandable

A few days ago, I came across the idea to build a new htpc with an iMac as basis.

With Windows XP or Vista via Bootcamp installed, it should be a really great alternative. My tv cards would be moved inside my server so that the iMac would "only" be a client and so eliminate the need of not existing pci slots.

But, before I buy it, I want to check if I have thought out all things correctly.

The iMac would be connected to a 40" lcd screen via hdmi and via spdif to a creative inspire digital soundsystem (with a more or less receiver) (later maybe a "real" receiver+speaker set). Currently, my htpc has a special sound card with live dolby digital encoder, but I am not really sure if I really need it. Would an upmix of the soundcard or of the receiver be better? And, what does have maybe an even greater priority...If I upgrade to hddvd/bluray via an external drive, could I use spdif passthrough or is this not possible anymore with the new formats etc.
With a ddlive encoder, anything what can be played on the pc would be sent through spdif too.

Or did I have a hole in my plan that I did not realize? Please I want opinions ^^

Pharao2k