Switch out to MRV.
It should cost $99 and they swap out like equipment.
You tech will bring an HD reciever to swap the standard and unless your current DVR is an R16 or R22, he will have to bring a new DVR.
Most techs try to bring a R22 for MRV since it is the only MRV compatible DVR.
If he does bring a R22, then when he activates it, because you already have high def, it should take the HD download automatically.
But double check and see prior to arrival if it is. Also, it does not hurt to have them put it in the notes (won't guarantee an R22 but will help you get one if one is not available to the tech).
Basically, end result it is an R22 will be 1 HD DVR that you already own, 1 standard DVR that will end up being hd, and 1 high def reciever and you being able to watch recorded shows on all 3 TV's
If he brings an R16, you can should be able to call after and get them to send you an R22.
But you need to call immediately.
Total cost should be $99 + $3 a month or you could just swap the current DVR for $99 and get a lot less service but save $3 a month.
BTW, also tell them you want a Broad Band Deca so you can get video on demand and DVR to PC. (this will be free)