Only a few days in but very happy with this dac/amp. It's my first venture away from on-board pc sound and with a decent pair of headphones (DT770 custom studios) there's a marked improvement in all round clarity and smoothness, as well as having much more volume available now. I'd say the sound stage is wider now also and as there's no distortion the whole package sounds much more refined than using my pc's on-board sound chip did.
My headphones are 80ohm and in either high or low gain setting I've not had the vol dial past 12 o'clock - that is already plenty loud enough and I'm sure this amp will easily drive higher ohm headphones if I wish to purchase some in the future.
I'm on windows 10 and after first installing the drivers from Audio GD's site everything worked flawlessly. The build quality looks very good indeed and so all together, I'd thoroughly recommended this product and also Audiophonics who delivered it within a week to the UK - very good service and I would certainly shop with them again with confidence. Many thanks.