I kind of answered my own question. I tried this configuration out today and it works perfectly. Media Center is able to send an isolated signal to the appropriate set-top box. I can then run the output from each set top-box to separate analog tuners and record cable. I'd prefer that the channels were still clear QAM, however, given the cable company's desire to spoil all things good in life it doesn't look like clear QAM will be available in my area until some new provider decides to take over the local market and treat its customers fairly.