Apologies, joking aside, I don't want to leave your questions unaddressed, especially with you being (relatively?) new to Head-Fi
In order to help you better, it would be helpful if you could tell us what you liked and disliked about each of those AMP units?
Also, do you plan to mostly use the AMP single-ended, or with a balanced cable? (can explain these terms if you don't know them, but I'm assuming you do!).
My general impression is that AMP1 is relatively more reference and neutral sounding. AMP3 a bit more warm and organic, AMP5 even more warm and organic.
AMP2 seemed to have a somewhat richer and intimate sound, but more subtle and rather different from AMPs 3 and 5.
I've read some differing reports regarding the bass quantities of each. And my reviews are based on past impressions that I may have remembered imperfectly, since I've mainly just stuck with AMP3 so far just for the sake of convenience (all my IEM's are using balanced cables now).
I haven't yet had the chance to try AMP4; potentially that could be a winner?
And, joking aside, if you were willing/able to shell out for a DX150, that comes with the new AMP6 that may offer a similar, but possibly improved or at least slightly different sound to the AMP1 - and it's confirmed as being compatible with the DX200, and has the same single ended and balanced outputs as the AMP1.
Hope this all helps, and feel free to let us know more about what you are looking for