The HR34 is SWM only. Given that you have an R15 on your account, you do not have SWM (the R15 won't work with SWM). So in order to get an HR34 you would have to convert to SWM.
If you drop the HR20, keep the HR21 and get the HR34, you would have 7 tuners which will work with an SWM LNB or with an SWM8 switch. However the R15 won't work with those (actually, it could run off an SWM8, but I don't think DirecTV supports that configuration).
If you swap the R15 for an R16 (which is SWM compatible), or for an HD receiver or DVR, then you would need an SWM16 in order to handle the total number of tuners you would have (more than 8).
Another option would be the HR34 plus a C31 RVU client and the HR21. Replace the R15 with either the C31 or the HR21 (and put the C31 where it was).
If you drop the HR20, keep the HR21 and get the HR34, you would have 7 tuners which will work with an SWM LNB or with an SWM8 switch. However the R15 won't work with those (actually, it could run off an SWM8, but I don't think DirecTV supports that configuration).
If you swap the R15 for an R16 (which is SWM compatible), or for an HD receiver or DVR, then you would need an SWM16 in order to handle the total number of tuners you would have (more than 8).
Another option would be the HR34 plus a C31 RVU client and the HR21. Replace the R15 with either the C31 or the HR21 (and put the C31 where it was).
