when mastering the most important factor is keeping the references as consistant predictable nonvariables. even if you have the flattest nearfields in the deadest room, it only takes one hard hit of a harsh frequency to make the hairs in your eardrum lay down. people try to counterbalance this by gradually making the music louder and louder. aural fatigue can make a seemingly simple process drag on for days. i think it's ok for a producer to do some mastering if it is a labor of love. but if it is interfering with the creative process i would move on to more music and leave the mastering to the pros. izotope is kind of a resource hog anyway. i like the fact that in nonlinear editing it is so easy to just add dynamics and eq to each and every track if you want to. that typically doesn't leave much for the mastering house to do if your mixdown is useable. the advantage a good mastering house has is they know the short comings and flaws of all their reference instruments. they can master a track on their genelecs and know what it is going to sound like on their home theater system and their car stereo because it's the same gear exploiting the same weaknesses every time.

 

i'm listenin to some of your stuff right now.
it sounds fine