Bryan, what you've described is certainly far from normal. Although rooms vary and can result in somewhat different settings for bass level, they shouldn't be as far off the typical settings as yours are. My EP500 settings are probably fairly typical, with the sub level control around 7 o'clock and the receiver sub trim at -2.
The first oddity is that the original 990 calibration set the sub about 20dB too hot. Typically, the auto-calibration systems don't vary(as reported in S&V, etc. tests)by more than a dB or two from a manual calibration with a meter, and may be the more nearly correct of the two. Pretty clearly that was a 990 rather than EP500 problem.
Then, not being able to calibrate to 75dB even with both the receiver and sub level controls set at minimum would indicate either that the 990 sub output was far too high even when cut to the minimum, or the EP500 gain was far too high(either input)even with the input level cut by both the 990 and the EP500.
Of course, the idea isn't necessarily to calibrate at 75dB(or any other fixed number)but rather to have the speakers and sub at the same level, whatever the number is. Since you can't reduce the sub 5dB more, the idea would be to increase the speakers by 5dB with the sub setting staying the same(in effect calibrating at 80dB)so that they're equal. This doesn't explain why the 990 calibration was so far off or why two minimum sub settings are necessary for this result.
