Cross-posted here and in the Bottlehead comparison thread:
I'm thrilled to report that my mainline is up and running as of this afternoon, and my early impressions are extremely favorable. Having sat back with my hd800's and listened through a sampling of my favorite tracks this evening (from Oscar Peterson and Jazz at the Pawnshop k2hd to Emma Kirkby and the Choir of St. Martins, and from Alison Krauss to 2Pac) - I have to seriously applaud the team at bottlehead on their new flagship. This amp is technically excellent and thoroughly enjoyable with every genre you can throw at it, and that is most definitely not a statement that I would make about many widely recommended "TOTL" headphone amps.
To provide something a bit more concrete - here are a few preliminary impressions of what I'm hearing in reference to Pierre Fournier's brilliant performance of Bach's Cello Suites. I've probably listened to this album a hundred times on various systems and can't ever recall hearing it sound this good. Transients are simply effortless - so fast and clean. Timbre is rich and lifelike, and the audible micro-detail and texture as Fournier digs deep into the strings on certain notes are absolutely amazing. More generally, on albums across the board, bass presentation is faultless - deep, impactful, and incredibly tight. Possibly the best I've heard from any tube amp? Trebles are detailed and nicely extended, but never strident. For example, I tend to prefer my crack with the anax mod in place. But to my ears, the pairing with the mainline doesn't need it and hd800's have more air without.
From a comparative standpoint, I will always love my crack (an incredible value which will soon take up residence in my office) - but for anyone who has been sitting on the fence awaiting comparisons, be assured that, at least to my ears, the mainline absolutely takes it to the next level.