Finally got my JH16 Pro FP back from JH Audio, and have been listening to ZX-1/PHA-2 combo with it. I actually went through the entire Duran Duran Greatest Hits album - yeah, I am not necessarily proud of this - before moving on to my usual assortment of high res Jazz and Rock tracks.
To make the long story short, the JH16s proved to be a great match for the ZX-1. I guess this is true in general with the JH16s, but there was just a lot of "good" bass - not boomy, but just "meaty" and fast - with these earphones even when the ZX-1 was unamped. I think whoever thought the ZX-1 was a little thin on the low end side should definitely try it with the JH16 Pros... With the PHA-2 added to the chain, I thought there was a marginal improvement (soundstage, mid-bass) to the overall SQ, but I could definitely live with the unamped ZX-1 with the JH16s. The somewhat pronounced bass presence did not take away from other frequencies, and both the treble (good extension) and midrange (overall presence) were very much enjoyable.
The JH16s can sometimes deliver too much bass with my old Fiio X3, and I often turn down the bass through EQ. With the ZX-1, I actually can stay away from EQ all together and be happy with the bass level/quality. Also, the JH16s reveal the ZX-1's ability to deliver better detail/resolution compared with X3, which I did not notice much with my "lesser" IEMs.
Can't wait to try the Roxannes on the ZX-1, if they ever get here... I know AnakChan mentioned that the treble could be a little piercing, so I am trying to manage my expectations, despite my positive experience with the JH16 Pros...
BTW, the Yankees finally got Masahiro Tanaka, and maybe, just maybe, they won't suck like a vacuum cleaner next year...