Hi W, I just purchased a new HiFiMan HM700 DAP, which came with a pair of RE400b's (balanced inputs), which I find a little too flat for my taste. I absolutely don't like bass heavy (boomy/bloated) IEM's, but do enjoy a bit of low end robustness and emphasis, achieved by design and not equalization.
After reading several interesting on-line reviews, I was considering giving the MA750's a try, particularly because of their robust and extended low end performance, but am having problems finding an on-line retailer, so I may not be able to get a pair to try out.
After reading you post, I believe the MA750's bass performance may be too much for what you seek though. I am comparing the RE400b's to an old pair of Klipsch S4's, which I always found had the bass performance I liked in IEM's, but the quality and clarity of sound on the flatter RE400b's set it apart and clearly above the S4's overall sound. I'm still breaking in the RE400b's, and with my HM700's on board equalizer, I may dial in the right amount of bass, and they may grow on me, who knows.
I'm an audio enthusiast but have only owned IPods for personal music listening up until now, and am new and a beginner to the hi end DAP scene. My HiFiMan HM700 in no way compares to your Fiio x3 with Wolfson DAC and dedicated amp on board, but I thought I'd chime in and provide my comments on the RE400b's.
BTW, I'm new to the forum, cheers.
*UPDATE- Apr 7th = It's been a little over a week since I received the HiFiMan HM700, and the RE-400b IEM's, and I have to say the DAP and IEM's go very well together. I've fully burned in the RE-400b's and the sound is very satisfying, very nice relaxing but dynamic sound-stage, very good channel separation too, probably due to the balanced HM700 outputs and Re-400b inputs.
I still find the bass a little attenuated for my taste though, so I made fine adjustments via the HM700 built in equalizer, and the sound is the best I have heard so far from an IEM's, although I have to admit the FLAC (16bit) files on the HM700 play an important role in the sound too.
The only gripe I have with the RE-400b's is the fitment of the tips, which I have yet to find one that fits perfectly, despite the bag full of rubber/silicone single/dual flange tips included, but that's more an issue with me than the product itself.
I will continue to test the HM700 and the RE-400b's with my usual mix of music genres, and report back when possible.
*UPDATE- Apr 18th = On my Apr 7th update, I thought I had fully burned in my RE-400b's, but it seems I had not done enough as after another 48hrs of burn in, the bass has loosened up and deepened some more, and I now had to dial down the bass EQ I had dialed in a while back, to balance it with the rest of the sound. The sound from these IEM's is so detailed that even with the bass EQ dialed up, the mids were never drowned out, and the staging now seems a little more open and airy too.
The truth is I am amazed at the sound these dynamic 8.5MM drivers put out, it seems as I have a much more expensive set of IEM's and not just a $99 pair. I was looking at getting another pair of IEM's with a bit more reach in the lower registers, but the more I listen to my FLAC rips, the more I am convinced I made a great choice purchasing the HM700 together with the RE-400b's. I don't even feel I would have gained much from choosing the more expensive option, with the RE-600's, so for those still undecided, looking for a very good neutral sounding, reasonably priced set of IEM's, go for the RE-400 Waterline's (without TRRS plug), or the balanced RE-400b's (with TRRS plug) if you have a DAP or amp with balanced output, I trust you will not be sorry.
Edited by Vic-CX7 - 4/18/14 at 7:54pm