Thanks Nirvana, I know I'm new here but I've had this setup for way over 2 years, and owned several different headphones (HD650, Denon D2000, Grado SR225i, Beyer DT880 for example) and amp/dacs previously. It took time to find exactly what I like and now I'm just trying to get the most out of it.  

Thank you both. I've never tried a tube amp with my HD600s, only solid state. I appreciate that more power will only improve the sound signature I love. What impact are tubes likely to have on it?  

If it helps, the upgrade paths I've been considering are:   1. Using the Fun's dac section to feed a better amp 2. Getting a better dac 3. Improving my source, but wasn't sure where to even start with this 4. After market headphone cable - although I'm dubious of the benefits, and even...

I have tried to work this out for myself by searching the forums and reading extensively, but there is so much conflicting opinion out there, even about the equipment I already own.   Please could some experienced members advise me - what ONE upgrade would they make to my current setup, in...