If you go to the info site, the filters are listed there.
I now have the Ember. Serial no. 0000 Yes!!! It is a very good, solid performer.
I'm using it with a modded T40 and an active filter to raise the top end; all made/modded by Frans. It is a LOVELY match.
The Ember can have it's gain changed by the owner and also the output impedance (along with the tube), so you can kind of tweak it to your liking.
The T40 is not a particularly easy load to drive either. Modded, it's slightly less sensitive than standard but really flat in frequency response. I have the Ember set at low gain and low output impedance and it drives the headphone like a portable. Dead easy to drive. It's loud at 11:00.
Not only is it loud, but the T40 becomes a lively headphone. There is plenty of bass presence and weight and it's really fast in attack. I have found that the T40 can be a little thin on some amps and often have wondered whether it's just not being driven hard enough. This amp sounds good with it.
The Senn HD600 is also very lively at low output impedance and low gain. 9:00 is loud enough this time. There is no Senn 'clouding' and they also sound extremely lively. TBH, the amp drives it as though there's nothing there!! It just goes with ease. There's way more power than you'd need, so plenty there for transient attacks.
In comparison to the Horizon (which I also have), it sounds perhaps less 'tubey'. I like the Horizon a lot but this one has serious power and makes headphones jump to life.
It runs extremely cool and so doesn't need the fins that the Horizon has.
I've been listening all afternoon (since it arrived) and am very pleased with what I'm getting; especially on my T40.
Any questions, just ask Solderdude, the designer, here where there is one in the UK doing a tour: