Hi Joe,
Welcome to the forum.
I owned the Grado SR60 for a while and had an
SR125i here for measurements:
What I found is they have indeed a very 'forward/open' and lively (dynamic) sound with at first glance a lot of details.
Thougt the SR60 sounded better than the SR125i as the 60 (and so the 80) has a bit of a bass peak.
In the end the lack of bass extension, treble (fine nuances) and lack of comfort is what made me sell the SR60 again.
Mids were actually good with a bit of 'over the top' forwardness.
About the sound altering properties of tube amplifiers.
When you have connected music to your guitar amp you may have noticed how different it sounds from a hifi setup.
The 2 of them (guitar and hifi) have only one thing in common and that is a tube.
Otherwise the properties differ more than they are the same and so are the requirements.
So what can you expect from a tube amp ?
Well ... that is kind of tube dependent and some tubes roll-off in the audible range.
Stock tubes do not.
Also when you look at the FR of the SR125 (same driver as 60/80 AFAIK) you will notice the somewhat exaggerated 'forwardness/openness/dynamics' lies in the 1kHz to 4kHz region (the peaks you see there)
The (fake) treble detail is partly caused by the 10k spike, this spike is narrow so won't be that audible in most music.
None of the tube amps roll-off before 10kHz so the 1kHz to 10kHz will not be 'mellowed'.
Of course it could still 'warm up' the sound but through another 'mechanism'.
There are 2 of them that do the trick and that is a high output resistance setting (also a good thing to counter tube noise) which, as you can see on the SR125i plot below has to do with an increase in bass.
green is 120 Ohm out, red = low output R (the plots are level matched, in reality the 120 Ohm setting will lower the level considerably)
As the bass is somewhat elevated our brains 'evaluate' the overall tone slightly (and I mean slightly) different and subjectively makes it sound a bit 'fuller/warmer' where the mids and treble are a bit lower.
The second mechanism is added harmonics.
You playing guitar will know the effect added harmonics have on the sound (effects or tubes being overdriven).
Well the effect for hifi differs a lot because these effects also produce large amounts of InterModulation distortion.
This isn't 'bad' for a single instrument that must distort but terrible for all sounds.
Hifi sounds awfull with too much harmonics added, certainly because there are a lot and they are high in order (well above 5th) as well.
For G1217 amps ther are added harmonics but not much, and almost none for low amplitude signals.
The bass and lower mids have the highest amplitude so they have more harmonics, but only low order (2nd and some 3rd) which isn't that objectionable.
As it is amplitude dependent and a high output R also means a higher output voltage needed the effect is a bit more as well.
As Grado's are low impedance and fairly efficient the SRIII and Starlight are both good choices.
BUT I would either change the high output R value (from 68 to 100 or 120 Ohm) or contact Jeremy (if you want one ready made) and ask him to change the 68 Ohm to 100 or 120 in your case.
The SR80 will still go loud enough but you will get more 'mellowing' what you seek.