Thanks nicolars and everyone for your help.
Sounds like the 1540 will give everything except the isolation.
I've had several strong recommendations on Yamaha HPH MT220 and DT150. Have you heard either of these?
No I havn't but seriously just buy the 1540 and ideally a good source as well 1540 + NAD D1050 are like they were designed to sound good together, the D1050 fixes all the weak parts of the 1540 from a lesser dac / amp (the weak parts are pretty minor anyway compared to most headphones, the SRH 1540 do it all with a good source, very nice bass, very nice mids, silky treble with a little bit of sparkle, imaging, separation, 3D soundstage, pace, comfort, build quality all accounted for. Perfect balance between "neutral / reference" and "fun"... If you get the 1540 you can upgrade the source later and experience high end sound at mid range prices. More people should seriously buy the 1540, Shure is such a great manufacturer, if you listen to a variety of genres and want all round sound quality with an almost open soundstage and closed bass at the same time, there are not any other headphones that can do that at the price (that I have tried anyway). Also if you want to go a bit cheaper the NAD HP50 and PSB M4U headphones are very popular, I have not heard them for long enough to give a proper opinion on them, except that the comfort and fit is bad compared to the SRH1540 and they have a smaller soundstage.