At this price, it is a steal. Matrix equipment competes way above its price point. This unit, just like the 3U/3A should work really well with the HD800.
PurkThe headphone out of the Quattro II is powerful, but a little on the analytical side of sound, in my opinion it pairs better with warmer headphones.
OstewartStill for the price it is a great great deal. Matrix has a nice and regulated power supply built in. I would buy this over CavalKi's designs just for that alone. I have the Matrix Balanced 3B and 3U and they are a rock solid product.
OstewartThe 3U is likely a better choice than 3U. I personally will buy the Quattro for its DAC capability and add the 3B to it for best performance at a relatively low price.