Well holy cow, I let the 7550's play all night last night while I slept, along with all day while I was at work. I've never been a big believer in burn-in, but my god did the bass wake up on these things! I can now say without question that these have more bass all around compared to the 850's. Sub-bass, mid-bass, impact, rumble, etc. And my god these things can take some serious power! Like others have already mentioned, in order to get the elevated bass I am having to feed them high gain from my E12 along with a big boost of 60hz and below on my EQ.
Adjusting the EQ to more tame levels of bass, they can and do sound very good. I still stand by my previous comparisons with the 850's though, except for the bass. Now after almost 20hrs of burn-in, they outclass the 850's in low-end for sure. But as odd as this may sound, after doing this comparison it has just made me appreciate the 850's more. I think I prefer them for overall sound quality and soundstage. The 7550's excel in the bass department, and with their less fatiguing treble they are easier to listen to at high volumes for extended periods of time.
Both absolutely FANTASTIC pairs of IEM's. I will be keeping both