Thanks, well I just received my custom earphones by FS! Right away I can tell there is more sub bass then the Universals and a lot more bass then all the other earphones I owned and borrowed. Still getting used to the shells in my ears. I have been using foamy tips which are so easy to insert. Also burning these customs in, I ran them like for 30 hrs as of 3 days.
I don't know if you've made your decision yet, but you want the MG6Pros. The low end is pretty stupendous. I use mine for monitoring on stage. I play bass. I need bass and I like bass that feels like it's coming out of the ground. Last Saturday night I played the Boulder Theater, which has some ridiculously huge (7 feet?) subwoofer cabs that are deep and tight. The MG6Pros were at least as good sounding, if not better. I have an EQ called an Alembic Superfilter, which is a state variable filter that can sweep down to a center frequency (or cutoff for a low pass, or cutoff for a high pass) of 45 hz with additional resonance available. Usually when I boost down there past a certain point, it craps out IEMs, speakers, subs, etc. The MG6Pro just rolls with it.
I also work as a location recording engineer and have been on a search for good headphones to use on location that reproduce low end and seal well. My previous choice has been the Beyerdynamic DT770s (which kept blowing drivers) and ATH-M50s. The Future Sonics make them sound incredibly wimpy in comparison.
My only complaint about them is that they aren't the most transparent transducers I've used in the high end range, but they are unparalleled for bass. I use the smallest vents. The mediums were too much and I haven't tried the large vents. I'm going to have to relax with the big vents and some reggae at some point.
I also have to point out that the FS service is really excellent. David and Dayna have been really responsive to a lot of questions and they turned my order around really quickly, despite going off to NAMM. I've been using their universal fit IEMs since early 2008 after stumbling on some used FS1s and then moving on to the various Atrios. I've also used Westone, Ultimate Ears and another brand that escapes me right now.
I love the Atrios, but this is a whole difference experience. I hope you've experienced the difference between the Atrios with foam and with the SofterWear sleeves because this is like that leap except way more so.
YMMV, LOL, OMG, etc.