I'm not sure how I arrived at this gain staging, maybe someone can point to me what I have set wrong.
 
I have all trims and faders set at unity, from track to bus to master to my hardware. No plugins inserted anywhere. The track shows output of -0.2, in the console view the track shows-0.0, the bus shows -3.0, the master and hardware shows -6.0. I have pan law at default (0db center, sin/cos taper, constant power. I can't find another setting that reduces level by 3db not once, but twice. Hopefully you can use the percent zoom in your browser to see pic detail. Thanks, Shep  here's a link, too.....
<a href="http://s156.photobucket.com/user/jshep0102/media/Meter%20Differences%20at%20Unity.png.html" target="_blank">   click on the magnifying glass for full size
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jshep0102
The track shows output of -0.2, in the console view the track shows-0.0, the bus shows -3.0, the master and hardware shows -6.0.

The console strips are not showing tenths of a dB that the track is because there isn't room with narrow strips, so that accounts for the -0.2 vs. 0 (not 0.0) on the track. The bus differences could be due to having a volume reduced in Offset mode. Otherwise I don't know what could cause that. Click the Offset/Envelope mode button in the Mix module to check the buses.

It would be useful if your screenshot were to show the In / Out module 

Any PC modules active?

I could also imagine a bus auto attenuating by a few dB since it's practically always used for summing, but I don't recall reading about this anywhere.

One clip playing (-0.1 peak) from track marked Kick. Kick out to Drums bus,
Drums bus out to Master, Master out to SPDIF. I never use PC. No offset.
So weird. This is a demo mastered to -.01. RMS still down -5.4db at final output.
 
EDIT - I sent the track straight to SPDIF. Exact level as track. I'm losing relatively
3db per bus. Good thing I don't go through 5 busses... Can't find why.
 

I have never seen that without something in the signal path causing it. 

I started this project from scratch. There are no plugins installed at all. The earlier picture shows all tracks and busses. Only going to 2 busses, then out. No sends, no automation. at all. I'm stymied where to look, John.

I deleted everything but the 1 track, 2 busses and SPDIF. When I put the bus outs to prefader, the Drums bus matched the track (but that's not showing what it outputs), but the Master bus does not because it doesn't come in as hot. When I bump the trim on the master 5.4 db, it is equal. If there is nothing on a bus including automation and fader is at unity, why would it matter if I use pre or post?

Does your RME 9632-Digimax have mixing software that could have some impact on levels? What version of Sonar are you using? On the Buses you have FX on. You appear not to have FX inserted but try turning the FX off. 

I'm on Lexington. The signal only goes to the RME after the master. I use no outboard gear. The RME feeds the Central Station. The RME shows the same level as the Master bus and Hardware out meters in SPLAT.
 
I saved the project and restarted Sonar. The levels are all the same with prefader selection on Busses now - which feels very good. Oddly, when I changed the bus meters back to post, only the Drums bus level lowered, while the Master bus still output fully... Can this be a bug?
 
After save and restart:

After changing to post fader, the drums bus level lowers, yet doesn't affect the master level: