The JH13Pro is a GOOD synergy with the HM601. Its strong lows and highs are great with it along with its slightly (read in comparison) recessed mids. Now, as to battery life, I've nothing good to report. The stock 2GB isn't enough if you want to go lossless, so you need to put an SD card into it. I bought an 8GB Sandisk (for next to nothing here) and it is great. Just update the files and go. All music integrates into the native finder of the player, but I think with the SD card, I get no more than 6-7 hours of music. I've certainly not gotten 8 hours.
Now the HPO construction quality could be better. It tends to grip headphones very loosely; at times they can pop in and out of their own accord. Also, it is plastic, not metal. I think Head-Direct could fix this and lend stronger grip to headphones.
For sound (minus the gapless) and minus the use with warm headphones, the HM601 is a great player. For battery life, it is a bugger. You can bring a mains adapter with you and plug it in to listen. I've detected no real rise in levels of hiss. Also, hiss IS more than iPod touch (of course that is pretty much lowest in industry right now other than the new iPod shuffle (next to nothing at all)), but it is MUCH less than any Sony, about the same if just a bit more than the S:Flo 2, and much much much less than the other Audiophile player every talked about: the AMP3 Pro1 and 2.
It isn't dead black with IEMs, but with headphones and even the AT CK10, it is almost black. Great player, Mido, but frustrating in its format support, lack of gapless, and battery time. Worthy? Yes, most definitely.