ok, so your WHS isn’t that

ok, so your WHS isn’t that power consuming, you’re correct that minimizing the number of drives is probably the best thing you can do to save some power.

Now, onto your configuration…I agree with you that the Extender’s just suck. However, if you do decide to go CableCARD, then you have as much concern about copy protection than system resources. If anything you record on your main HTPC via CableCARD is flagged Copy Once, then you will NOT be able to play that program on any other HTPC–only an MCX Extender connected to it would work.

Now, what you could do is go with something like the CETON or SiliconDust PRIME and then use the Network Sharing Tuner to associate a specific tuner to each system, but then that gets messy as each system would have to individually record the program.

So for starters, you need to decide if you’re going to be able to live with only watching some (if not all) of your TV recordings from only one system?

Btw, have you thought about boxes like the Roku or Boxee Box? Those are optimized video players that wouldn’t be able to play your recorded TV, BUT, they draw SIGNIFICANTLY LESS power than any HTPC you could build.