Project Ember

You might like the Sennheiser HZR62 then.
It doesn't colour the sound to my ears, though I have reduced the chord length to 1M.
The sliders occasionally get scratchy when a blast of Deoxit into the slider mechanism sorts things out.

Well that's the thing, when you are close up to a piano in a domestic setting it sounds more mono than stereo- none the worse for that though. When I'm listening at home I try and imagine I'm in the middle of the front row of a small concert hall or large room, like in those big country houses, and there's just me and the piano- I'm a frustrated player really!

They work well with orchestral imo Howard. The sparkle in the top helps string tone and the bass is quite deep and full as well. In fact, I'm listening to 'Composer of the Week' on Radio 3 where they're featuring Northern composers. (Icelandic) I'm going through the Ember now.

The depth of the DT990 bass really helps in those lower bassoon and lower string passages where you need the bass but also, the treble makes it easier to differentiate them.

250 ohms impedance means that there is zero noise from the Ember as well.

They're not a flash headphone, but they work well. Great at that price when you think, for a th900, I could buy ten of them!!!

One thing that many don't realise about the dt990 Howard, is that where you place them makes quite a difference to the sound. If you have a 'sharp' sounding recording, move them back on your head. If you have a 'flat' sounding recording, move them forward. The quality of the treble changes, depending on where you wear them on your head.

For me, low onto my jaw and forward gives a snappy response.

Coming from the Ember, you get that lovely tube warmth and an openness that is really excellent if you wear the DT990 forward on your head. If this were measured with a virtual 'ear' in place, the measurements would look very different.

The 'u' shaped frequency response kind of makes sense for low level listening imo. Monitoring headphones need to be flatter and are played louder so less of a 'u' is desirable.

Tyll has been looking at 'ideal' frequency response curves and it seems to be a fairly 'fluid' curve with different ideas as to what constitutes flat but having a skew at each end is fine if you listen at low volumes. I think listening volume and frequency response curves need to work together for the actual listening experience.

Received my TH-X00 today and have to say the pairing with the O2 is very nice indeed. Nice cheap option if you have a standalone DAC already.

The Grace M9XX does look tasty though if an all-in-one solution is preferable. Not cheap but seems well regarded.

I think in general some amplifiers can have problems with low impedance cans because of the high current flow demand. Hiss is my main problem with some low impedance cans. Some of my low impedance cans never hiss, others do. It seems related to the sensitivity and frequency outputs of the can as well. Those with higher treble emphasis seem to hiss louder-I suppose that makes sense.

Thankfully, with all G1217 amps there's ways to remove hiss. You can raise the output impedance, but that may colour the sound (not necessarily adversely though) and you can also use a lower gain tube. There's also the option of adding some sort of in line resistor between the amp output and the can, again to lower the power output.
I don't get much hiss problem with Polaris, it's a very quiet amp and only my cheap IEM'S hiss if I inadvertently connect them when the amp is set on high gain, which is inappropriate anyway for them. It's easily corrected by reducing the output gain by moving the jumpers.
Starlight in my experience is more forgiving of noisy tubes and is my choice for low impedance, high sensitive cans. Ember and Horizon are more designed to handle the higher impedance cans-though some lower impedance cans are excellent with them, eg HE400.