No restrictions for your choice, either. Just tell me the cans you think would be a good foil to the Sendys and why.
Modhouse Argons, I have mk2 but the 3 seem to be very nice too.
Both headphones need quiet some power and are great when used balanced.
The Argons have a huge soundstage and really great bass. They are also kind of closed.
The Nighthawks are also a nice compliment to the Aivas, because you can use the Aivas cable with them and they sound nothing alike. the nighthawks again have a much wider soundstage and change a lot with sources.
I previously owned a pair of Cascadia Audio Talos, which are another mod of the T50RP. Curious how much a sound signature difference there is between those and the Modhouse Argons.