Thanks, Charles. Is reverb supplied by the Ambience setting?
If you are using headphones, there are two versions of 'ambience' on the FP-90 (can't remember the menu settings for them):
One is a standard reverb - you stop playing, and you can hear it echo/reverb for a short period.
The second, it a type of ambience that I found quite immersing on my closed-back headphones... the problem with it is when you stop playing it just stops dead, instantly. This makes it a tad unrealistic and annoying.
Correction: Lowering the bass eq slider past what I considered "reasonable," almost to the lowest setting, did help with the booming bass. It seems that the bass slider is oddly calibrated, at least on my piano, but the important thing is that it helped balance things out.
In the menu system, you can adjust the crossover frequencies for each EQ slider. So, say you lower the bass slider... but find it is at the expense of some of the mid-range, you can make an adjustment. I'm not sure how much adjustment there is, but it's there.
RE Muddy middle octaves - I noticed it (at grade 1) playing some pieces above my grade, so I did the opposite of what you're doing - I lowered all of the resonances in order to get some clarity. It could well have been my lack of experience - I'd be interested in whether I still feel the same now.