Please bear in mind I have been a professional Stand Up Comic for 43 years and not a sound engineer, nor do I have 'golden ears' - I have 61 year old ears and am not qualified to give a comprehensive review.
Agree for the most part with what @lycos has to say. First up; the German build quality is second to none. It 'feels' solid and the motorised volume pot is worth a mention. It feels like a volume knob should and can be slaved to any remote. It also has a small LED in it which is a nice touch to indicate when it is on, as well as the gorgeous VU metres. It is a balanced amp and in short, it is the best Headphone Amp I have heard. It really does have the utterly silent background some amps claim, almost palpable - I have turned the pot up enough to deafen someone if anything was playing and absolutely nothing. There is a switch for higher impedance cans inconveniently located on the bottom but I have never had to use it; the LCD's sound awesome and it is a great match for the HD800's, which I can find bothersome even with the SD mod on some chains. You may have heard this about other amps, but this thing really will make whatever headphone you use with it sound it's very best - bear in mind, I am going by what I own and the cans I auditioned it with at Addicted to Audio. The sound: firstly, I find many tube amps a bit gooey for my taste and I listen to a lot of classical and prefer fidelity over comfort if that makes sense. From what I have read from lot's of research over a long time on SBAF the DNA Stellaris would be the ideal tube amp to my tastes - but it is a too costly and too far away. For a solid state the Phonitor XE is plenty warm enough, especially when coupled with the Schiit DAC.;I think this combo really hits the sweet spot. The amp has great separation of instruments and vocals and perfect channel balance - which can be adjusted anyway which is a bonus for people with hearing issues. This coupled with the Yggdrasil's reverse phase option has every conceivable base covered. The trebles are crystal clear, on lesser amps David Gilmour's voice can sound a little sibilant; but not with the XE and the bass is everything I need even with enough sub bass to compliment cans like the Audeze - again to pink Floyd; when the heart beats on DSOTM or the opening chords of the Beatles 'Come Together' you can almost feel it in your chest as much as hear it.
The Crossfeed function actually works better than most as the Phonitor line were designed for studio listening. Let me say this though, even at max settings, I didn't put it on and feel like I was suddenly transported to a hall with the instruments all in front of me. We are not talking like the first time you heard Bowie's 'Station to Station' on a quadraphonic kit in the 70's. I do think it would probably cut fatigue down though and while still retaining enough of the above mentioned qualities, probably delivers a slightly more laid back presentation to my ears. Mind you, I am someone that enjoys the 'super stereo' effect of a Head-Fi set up.
It has Headphone inputs on the rear also, so you can if you wish leave your favourite cans plugged in without front side clutter.
As mentioned it has channel balance correction options.
You can only use one set of Headphones at a time. It does have a single end option but if two cans are plugged in it will default to the SE which I find rather peculiar. I also have it on good authority that if you remove a SE connector while it is playing it will basically blow up! This is not something I would do anyway, but it is good to know about.
The two dip switches are located on the bottom of the unit, which is not light and so are in a fairly inconvenient spot. I have never had cause to use them, but even so.
As mentioned, the paint starts to fade around the functionality switches after a comparatively short time. Not something that worries me, but for a higher end unit I can see other people being annoyed.
Sorry for my amateurish review, hope you get something from it. Reader's Digest condensed version - I love this amp and am not looking to upgrade, which for me is something. It makes all my red-book CD's sound like SACD's. 🙂