Re: buying a used amp
In my dealings I've found that with used gear it doesn't really matter the number of owners and price is going to be defined more by condition, collectibility, and rarity. You might be able to talk him down on the price because it has had two owner. You can come at it from the angle that he doesn't know exactly what problems there may be because he doesn't know how well the original owner took care of it. Or something like that.
Price wise the DRRI is $1050 and the HRD is $730 new. Now lets assume both amps hold 70% of their value on the used market. DRRI= $735 and the HDR=$511. So yes it is possible for the DRRI to cost more used than the HDR new. Whether it is worth it or not is up to you. Both are cool amps.
EDIT: A quick search of eBay's completed listings the DRRI sold for $760 (+55 shipping), $700 (+50 shipping), $600 (+50 shipping), $730 (+45 shipping).