Any suggestions on an amp around £300 ish mark, could go higher if sound quality scales up accordingly.. I listen to RnB/Hip-Hop, Dance/Electro, some acoustic now and then. Edited to add, source will either be my PC, or Cowon D20, and I don't have a DAC. My source files are a mixture of flacs, wavs, 320kbps mp3 (and lower).
Portable or not? If not I'd take a look at the Lake People G103 (maybe G109 which I once had) as amp-only options or the Fostex HP-A4 as a USB-powered DAC+Amp that pairs quite well with the TH600. The AK10 (or its variant sold as Beyerdynamic A200p) might be a portable option though I did not hear that with the TH600 so far.