Great question; appreciate the candor.
I've been recording live music and mixing studio tracks for a long while, now ... about 20 years, and at the "prosumer" level.
Short answer ... research the Shure SE535 if you want a pretty damn accurate/neutral universal IEM; I've been using Shure mics for years and the pedigree of their upper rank IEM's does not fall far from their traditional approach of catering to music creating professionals (ie > neutrality first, accuracy first while designing a driver set that can be EQ'd from here to kingdom come should one want to experiment with different sounds.)
Also, the upper end from JH Audio (should you desire to move beyond the 500 dollar mark) cannot be overlooked. Seems I remember a Head-fi.org front page notice that JH Audio is producing a new IEM *specifically* for audio mastering purposes but for the life of me I can't find the add ... but just check out their website.
But for the 500 dollar range? And specifically for audio mastering/production, I can unabashedly recommend the Shure SE535 (or even better if you don't mind non-detachable cables) the Shure SE530 which has the same driver set but no detachable cable ... and it can be found online in the 250 dollar range (the best deal in IEM's in my opinion but then again I'm biased by my music production background). Another aspect of the Shure 535/530 IEM's that I absolutely love is the fact that they retain their solidity and discipline to insanely high volumes; this is more so because I enjoy demo'ing tracks under a gazillion different listening scenarios, among them being, Uber Loud(tm) ... than it is because I actually enjoy listening at perforation levels ...
... and the Shure's just go and go ... never heard any distortion, no matter the forced volume ...
Good luck.
.joel
PS : no personal experience but I've also read a lot of good things about the sensaphonic phones.