Let's say you sell the Linksys units for $100 each. Can you build an HTPC for that?
I would like to see the parts list.
The best would be for you to keep MKV's for playback on the TV connected to HTPC, and convert the MKV's to extender friendly format for playback on those. Chances are that your extenders are not connected to an extra large TV with preceicelly tuned sound system. So, there is no need to play high rez files on those.
Also, with the extenders, if you go the OTA route, you will be able to share tuners, just like you did with Ceton. Meritline has their Magyca tuners on sale today for $17.99 shipped. Get 4 of those and you will be set with OTA.
6 TV's in the house on FiOS and we only pay $4.99/month to connect them all!!! Power to the CableCard and WMC7!!!