I have DD 5.1 and don't have room for DD 7.1 and I have Klipsch Reference Series Top Of The Line Speakers with 2 Downward Firing SVS 12" Subs on a Subdude and my System Will Rock Your World with a Denon AVR-5803 170 Watt Receiver so I don't think you need DD 7.1 and I have Never had a Complaint about my Audio Sound!!!
For me, DTS-Master Audio and the Uncompressed Dolby makes a bigger difference than 7.1 speakers. But that's just me. But it's one of the things about the receivers, an excellent one can't do something just because it doesn't have the right port.