OK, so overall I'm pretty happy with the raised speakers.

There is a bit of a "hollow" sound I noticed immediately (like a dip in the upper bass) but I'm having trouble quantifying it and haven't had time to either do any A/B testing or go back to albums I listened to in the last day or two before raising speakers...

... so I'm not 100% sure the hollow sound is a real thing yet. Thinking about distances and speed of sound it doesn't seem likely that raising the speakers a few inches (5") would be enough to muck up response in the few hundred hz or higher range, but no time to really think about it right now. What I do hear clearly is just enough bass reduction to cut down a bit of a boomy edge I was hearing previously - but what I'm not sure is whether that same change is also causing the 'hollow' sound.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8