6007 power is 110w. 7015 is 125w
I re set it to factory defaults and went through Audyssey from scratch.
The power output difference is so negligible, you just have turn the volume down one click. If you are sure the settings are the same as that for the 7015, then may be your current/voltage need is at the limit and the 7015 might therefore just make it for you. Chance for that scenario is slim, but still could be happening. I think something else (other than the 15 W difference) is at play.
125/110 = 1.14 times, that is 14% difference, but in the dB (log scale, how people hearing follow) that's only 0.57 dB, for D+M AVRs, one click on the volume if 0.5 dB.
I am suggesting that the 6007 would give you exactly the same sound quality, but if you can duplicate the settings as that you make on the 7015, then you should be able to enjoy it while waiting and not getting "hollow" sound whatever that meant.
Obviously I am referring to direct/pure direct mode, if DSP functions, including Audyssey, then the two could sound audibly different for sure.