What's the deal with HT receiver gain levels?

That doesn't seem correct. I suggest you set the level of the 105 for one of the channels that doesn't go through the preamp to 75 dB SPL, using a sound level meter. Without changing the level of the 105, set the level of the preamp for a channel that does go through the preamp to also be 75 dB SPL. Mark that level on the preamp as unity gain. For 7.1 HT, use the level (volume) control of the 105; for non-105 sourced stereo, use the level control of the preamp, but don't forget to reset it back to the mark for HT.

You may want to set SACD output in the 105 menu to be PCM, so speaker distances and crossover are active for multichannel music.

I use the procedure outlined above in a setup in which analog stereo from an Oppo 105, a Sony XA5400ES, and a Parasound JC-3 phono stage go through a JC-2 analog stereo preamp; surround channels from the 105 go directly to amps and SW to a bass manager for a pair of subs.

It's easy and the sound, whether stereo or multichannel, is superb.

db

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?

I recommend you visit the Oppo 105 owners' thread at AVS. Post 8934 provides a good explanation of setting speaker levels with the 105. Whether you use SE or XLR should make no difference other than XLR being 6 dB higher. THX v line level outputs? Why would you pass video from the excellent 105 video processor through an Onkyo receiver? What is Int? Your setup seems overly complicated. The 105 has an HDMI input on the rear as well as a couple of other digital inputs; it does not have any analog inputs. Is the receiver what you use for amps? If so, why not just go HDMI-2 from the 105 to the receiver for stereo and multichannel audio and HDMI-1 for video directly to your TV or monitor? That's the simplest and probably most appropriate setup.

db

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).