The Audio Space Ref 3.1 has been making sweet music in my system for the last two months and I have fallen heavily for it's tubed charms. The full review is published in the Nov 08 edition of Affordable Audio (and linked directly in my reviews list sidebar here) but I can say that I've not found so much pleasure in any other component at this price. It's heavy, it's beautiful and it really makes sweet music. I'll be sorry when it's time to send it back!
Later footote -- too late for the A$$Audio review, I tried this with my new Virtual Dynamics David speaker cables. It's a tight fit round the back with these cables but the increase in bass articulation is noticeable from the first. This amp with Davids is just one sweet combo....I hate to argue for these expensive and heavy cables but there is no doubt that on everything I've tried, they work. Any doubts I had about the Audio Space's ability to articulate well in the lower regions are removed - this amp is just first rate. $3300 and you don't need a preamp!