I don't think the P-200 will be much of an improvement on the DA-200's headphone output, it's pretty good but it remains a bit below the P-1u. I only heard the P-200 briefly in the store though but I owned the DA-200 and P-1u. I'd recommend a used P-1 or P-1u instead of a P-200, it's in a different league.
Or check out some tube amps, I strongly prefer some of those over SS amps.
The DA-200 will drive all AT's and most other closed phones with ease of course but it did a good job with any of the Sennheisers I had at the time as well. The K701 is a different beast though you need a pretty powerful amp to make that thing sound good. Don't look at it's impedance (62 Ohm I believe?) it's really hard to drive it well.
Unless you really want 192/24 the DA-200 is a really good sounding Dac. I preferred it's sound over the PWD Mark1 I had as well.
For a 192/24 Dac take a look at the TEAC UD-H01, you could be amazed by this little cheap thing. Not as refined as the DA-200 of course and not much of a headphone output though.
My next Dac is going to be a Marantz NA-11S1 when it comes available next spring.
A Marantz NA7004 might be worth a look but it's 96/24 as well, sounds pretty good as well but doesn't come near the DA-200 though. It does cost quite a bit less.