You are just going to have to bite the bullet, go with the new setup completely or dump it for cable or Dish. I have had the "new" DTV HD setup for over a year now and had to give up my Tivo to do it. I had concerns, but the new DVR is not bad. It is worth it to get all the stations in HD and to get my locals over SAT in HD. Plus there are other features to the box if you connect an ENET cable. You can use it to browse photos, music, videos from a PC and even download PPV movies over your ethernet connection. Also, you can add an external SATA drive for more space. And it does have serial control, but I don't think the protocol is the same as the old boxes. I was happy there was already a CQC driver for it.
I concur with what was said above about the install. Only 4 coax needed. One thing to be careful of is the multiswitch you use. I had one and had bought another that worked in my Superpro panel. Neither supported the frequencies of the new setup. The installer brought one, and a quick search on the net, showed that only that one model of multiswitch worked at the time for the new setup. Also, it didn't require external power which was a nice bonus. The dish is much larger than the old one and will not fit on the old post so that has to be replaced. It has two front legs needed to help support it in high winds that must be bolted to the roof.
So you are probably better off just letting DTV install it, since they will bring the right equipment and accessories for free. You can choose how much you let them do. On my first install, I had an idiot, so I just let him align the dish and I did the rest. My last install with the HD setup and HR20 I had an excellent installer so I let him do a lot more.