Documentation and tests in reviews (in some places, they actually drove the 805 for a 4Ohm load at 270W, one channel at a time). Here is a link to one (I never bothered finding the other references back, this one is getting handy) http://www.hometheaterhifi.com/volume_14_3/onkyo-tx-sr805-receiver-9-2006-part-5.html.

Yes, ambient noise can be a huge problem. 75db for pianissimo is actually a bit loud (you have to consider the composer's intention too! \:\) ). 75db for "piano" makes more sense (that is what I have in my place). We would need a recording we both have to make sure we are talking about the same thing!

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