For reference...
The Onkyo TX-SR805 is equivelant to the Integra DTR-7.8 and the Onkyo TX-SR875 is equivelant to the Integra DTR-8.8 (the unit in question). I have seen both the Onkyo and Integra units and can personally atest to their build quality being solid, in line with any other receivers aside from a few specialty brands. The TX-NR905 has not Integra equivelant listed on their website. People have confused this a few times. The DTC-9.8 is a preamp only, and at this moment there is no DTR-9.8 (which if there was would be the equivelant of the Onkyo TX-NR905). I believe that Onkyo/Integra figures the Integra line's top end model should be seperates, not an AVR (hence why there is not an Integra DTR-9.anything).
To compare the Onkyo TX-SR875/Integra DTR-8.8 to the Denon...
Both the Denon and Onkyo/Integra feature network interfaces along with a USB port for streaming from an USB device. There have been a lot of complaints about the Onkyo/Integra networking abilities, Denon seems to have a much better track record in this regard. I like the look of the Onkyo TX-SR875 over the Integra and Denon. If I had to pick between the Denon and Integra for looks, it would be the Denon. For build quality (quality of parts etc...), the Integra would be the sure winner (may be the same as the Onkyo, not verifiable by me either way). They offer similar decoding and switching abilities with proper amounts of expandability. The Onkyo/Integra units probably have an edge in power as well, but not likely enough to be a big concern, if at all. The Onkyo/Integra are THX Ultra II certified, which means their amplifiers are stable with 4 ohm loads.