what are your thoughts on the momentum range anyone had any experience with them?
the on ears? if you can get them for a slight increase in price over hd25-1 II's then they are worth it otherwise just buy hd25's. they are basically a better looking HD25-1 II, far more stylish, some people may think that's worth paying the extra for.
the overhead version? i think there are better options out there for the money.
as for DAC's if you get the epiphany acoustics one, I don't think there is any point in you stocking anything else under £200 unless it offers different functionality like a fiio e17 (portability and multiple inputs).
all DAC's under £200 are pretty much on the same level as the O2 and Schiit Modi, the differences are negligible.
amps on the other hand you could stock a range to go with the O2, because different headphones require different amps and impedance matters more here over power. You have to get the correct impedance for your headphones.
I think you divide the impedance of the headphone by 8 and that is roughly the number the impedance of the amp should be. Take the Fidelio X1 (very low impedance at 30 ohm) requires and amp with around 4 ohm or less anything greater is unsuitable.
Whereas the Beyerdynamic DT770 250 ohm version requires an amp with around 31 ohm or less.
So i recommend you only stock 1 or 2 home use DAC's under £200 and then 1 or 2 portable use DAC's under £200 (fiio e17 and fiio e18 are well regarded as are others I bet).
When it comes to amps you will need a bigger range to accommodate all types of headphones or to accomodate the headphones you are looking to stock.
Take a look at this post here:
http://forums.overclockers.co.uk/showpost.php?p=26248873&postcount=588