Depends on the repair company. Some of them are so overloaded it takes forever for a repair.

As far as should you sell Denon, yes. Will you always have problems, yes. I have issues with every brand, Denon, Marantz, Pioneer, Onkyo, Integra, etc. The only brand that I have a track record of the least problems is Yamaha, specifically the Aventage line. They're just built really well and I don't have to worry too much about them.

Their OSD sucks, they don't sound too different or that great to my ears, but they just seem to work as intended after I install them and don't hear from those customers very much about AVR related issues... aside from IP control of them, but I abandoned IP control on AVRs long ago.