Summary: I bought this amp because it is stereo, simple to operate, and has a built-in DAC. It sounds remarkably good and would be suitable for use in a stereo entertainment center system. However, because of an audible transformer hum (present in 2 different units I tried), it is not suitable for any environment where you will be sitting within 8 feet of the amp if you have good ears. To me, this ruins its audiophile appeal. Extremely frustrating.
Summary: This Onkyo amp has so much promise, and when I first got it I was excited about it. I let it burn in over 100 hours, and I just could not eliminate the persistent hum it has. This actually interferes with quieter passages of music, such that I had to return it. Not sure, as other reviewers have said, whether this is an inherent problem with this Onkyo. I tend to think not, and yet I also don't want to try another unit either. I am done with Onkyo.
Summary: I went through two units, first one refurbished, second one brand-new. Both had the same problem with noisy volume knobs and 'silent noise' when i cranked the volume to max on a silent track -- though the brand-new unit showing less symptoms than the refurbished. I got the same noises whether using optical or coaxial/RCA inputs. I then checked the connections, power cords, etc. to make sure there was no interference, but the symptoms persisted.