I currently commute daily with GoVibe PortaTube+, CLAS and an IPod, though I am using IEMs. I have demoed the unit with LCD-3s and was quite impressed with their ability to drive the large unit, but note I did not have more than 1 hour with the combo so I can't critically comment.
The main issue I had with this set up (and it was minor quibble for the most part) was that I thought my IEMs (ACS T1s) had a dip in the midrange response. I could live with this, since a) it wasn't pronounced and b) compared to the absolutely incredibly tight bass response the T1s have, I though "well, midrange was likely to pale in comparison anyways". I needed to have the PortaTube+ serviced a few weeks back. Once the unit was returned to me (after just a few weeks; thanks Jaben!), the midrange dip seemed to be gone and a much flatter response in its place, while still keeping the awesome bass and treble inline. Not sure what GoVibe did or replaced but the midrange dipI heard was not the IEMs but seemed to be the amp. The unit was repaired under warranty at no cost (almost 1 year after purchase; thanks GoVibe!) but I never got a list of what was updated/repaired. Just something to look for in you evaluation of portable tube amps.
That said, I cannot compliment GoVibe and Jaben enough for the service and overall quality of sound (and enjoyment) I get from a small brick which fits neatly in a shoulder bag or a (large) jacket pocket.