What's the deal with HT receiver gain levels?

More data:

I listen to 2 channel via XLR, from Oppo to Int, with Oppo volume control set to 100%. This should be industry standard XLR "Line Level"?
Setting Int to level 60 borders on uncomfortable listening.

For video, I use HDMI from Oppo to Onkyo HT receiver and use pre-out to Int for L/R channels.

Setting Int to unity gain results in uniform volume
compared to speakers driven by receiver -so this is not the problem.

The problem is the obvious stress on SOMETHING (Integrated?
Speakers?) caused by cranking the Int to this level.

Since the Int is being driven by THX level outputs (pre-out), it seems obvious that the THX signal level is radically less than industry norm "Line Level".

I'm just wondering why the heckfire "they" would choose to do this?

DBPHD: The whole point of merging HT & Stereo system is to take advantage of the superior amplification provided by the $6500 integrated amp and the $8000 speakers for L/R duties.

It doesn't seem to be working out so I've decided to "un-merge" the whole thing and run functions separately.

Thanks for your interest and good suggestions.

P.S. I will try connecting my video monitor directly from the HDMI-1 of the Oppo and see what happens (a recent post of mine indicates there may be problems doing this, however).

No problemo...