I know there has been a little bit about these headphone amps so far, but i need more advice. I am about to order one of these gadgets over the phone (where i live no-one seems to stock any decent bass gear). I want to use it primarily with an electric upright bass that has no accoustic chamber and sounds like a big fretless. I would like to use it with a precision and jazz bass i have as well maybe. Which headphone amp really has preamp capabilities? does the mid range of the raven labs tip it in their favour? is the sadowski preamp sound really all its cracked up to be? any help much appreciated as i am not a gear junky and won't be making a purchase of this extravagence for quite some time. so want to get it right!