If you get the chance to run the Utopia direct from the XLR outputs of a high end DAC, then you might find its performance leaps upwards significantly. It did for me. Requires a very good DAC with a excellent volume control implementation, especially for a relatively sensitive headphone like the Utopia. Not all DACs support doing this - best to check with the manufacturer.
Anyway, my experience has been that the very best head amp I have heard is no head amp at all. If you haven't tried this with the Utopia I highly recommend giving it a go.