I purchased PK1 and PK2 only few months before MX 580 and MX980 materialised. Bad luck.
Today I would go the Sennheiser route, with noticeably cheaper pricing, also taking into account that these are easily available from any reputable retail or online store, with full back-up in warranty issues. In case of any defect on a PK2 or PK2, it hardly would be worth to send them at own cost to China for repair or replacement. The same applies when ordering spare foams, tips or clips for Yuin. It is way cheaper to cannibalise a brand new KSC75 than to order spare clips and foams from Head-Direct ($55, incl. delivery to Europe).
On the other hand I am reluctant, having already sunk the money into Yuins, whether an upgrade to Sennheiser MX would make sense. I mean, there are some members you did not like the MX. Still I prefer the Yuins' stealth design over the MX980' blingbling. Damn BMW design (I prefer Mercedes anyway...). Apparently the product manager in charge thought that was necessary to better justify the price to the general crowd.
I also considered Yuin G1A and G2A. In principle I prefer the fit of the PortaPro (the pods that rest on the temples), but it looks weird on your head and it does not fold flat. G2A with iPod Nano should work very well, with the Nano being very easy in your pocket. But when looking at the complete package, an iPod Classic or Nano with Headstage Arrow (or similar) with any earbud or IEM is about the same bulk. And the IEM or earbuds are less visible and attention rising than the G2A.
Relief came from an unexpected side. From my local (!) audiologist I got a set of custom tips for my RE0, at the same price as a new MX980 (cheapest online seller). Without asking, the lab installed an ambience channel into the tips, i.e. a channel connecting ear canal with the outside world. The tips did not improve bass or speed, but the RE0's mids and efficiency. In other words it plays lowder and fuller with unamped sources! Fit is both firm and comfortable which is great when you are on the move. The ambience channel makes you hear the environment better. Overall, iPod Nano plus RE0 plus my (!) custom tips is a perfect combo for walking arround. Be aware that the impact of custom tips depends very much on shape and material. Still, for stationary use and noisy environments I prefer the RE0 with single-flange tips and amped.
Edited by zappp - 7/5/10 at 7:20am