I think Markl is right on spreading the money around on your system. There are alot of good CDP's for less than 500.00 out there. Team one of them with the Singlepower MPX3 that Tuberoller has reviewed recently or with the ASL OTL32, and you will have a really good headphone system. I would check the Gear for sale or Audiogon for a Planet 2K or something along those lines for 500.00 or less.

I am using Corda HA-1 and the sound is better than creek obh-11se that I previously owned. It is smoother, and has better vocals. Creek is warmer,though.
I have not heard the HA-2, but reading from the reviews, you can't go wrong with it. You can also go for corda ha-1 and have kurtw modifies it to corda blue, it is approaching the ha-2 for less $$.

Whichever way you go for, I believe point of diminishing returns start from $600 dollars amp onwards. Like ha-2 prehead and so on. Amps below that like creek, x-can are all easily distinguished from each other even by an average-joe's-ear

Thanks again, all. Good discussion, this. As I mentioned in my initial post, I do intend also to upgrade the source. My current sources (besides the iPod) are a Denon DCM370 and an old but brick-solid Kyocera with an ART Di/o DAC. My plan was to give the Philips 963sa a spin, both to see what the SACD fuss is all about and because most everyone seems to think it has excellent redbook playback.

I've always been a "neutrality" guy, going for speakers and amps that seemed to give uncolored sound (if there is such a thing). But I think it's time to give tubes a whirl.

Everyone has commented that the MGHead OTL is a great match for the HD600s. Does it also mate well with the Etys? Or should I be looking at a different amp if I want to alternate between those two sets of headphones.

One word....Gilmore!

Don't know about the Etys, but with the right tubes the MG Head is magic with HD600.