So I got the T90's in the mail yesterday. They sound absolutely gorgeous with the Bottlehead Crack. Deep bass, liquid mids, and the treble extends really well. However I know you said that's not an option since you're in Europe. I'm currently at work listening to the T90's on my Aune T1 and I'm really surprised how well it sounds. I was expecting the T1 to have a lot of treble emphasis with these cans but thats not the case at all. The treble actually seems rolled off a bit. Bass response is good, not as deep and with as much slam as the Crack. It also doesn't have the warmth and body that the Crack has but the T1 may actually be a really good option if your friend is looking for an amp with less treble emphasis. It's also a really inexpensive option, I think I picked mine up for $130 a few months back.
Setup-wise I'm using the T1's tube dac and running an Amperex 6DJ8 with the gain settings on the T1 on low. It actually had too much gain for the T90's on high.