I've not heard the MF, but there are two other amps in your budget that you could consider - the
Headsave Classic , built in Canada, about £100 (inc shipping and a PSU), a lively and detailed amp which is truly excellent value for money, and the
White Noise Audio headphone amp, built in Scotland, about £200 assembled and tested; this is a very sophisticated and high quality amp. Both are meant to have great synergy with the HD600, and possibly outstrip the MF for sound quality (certainly, I have read posts by other owners that claim this).