So for everyone in the future, the customer service just replied to me that the "S-Balanced technology" is used on all the 3 outputs of the ifi iDSD nano BL. Sounds great to me. EDIT: My question still stands. How should I do TRRS to 2x XLR-3 from the nano BL to my amp?

Their website seems to be down for me today for some reason. I'll ask them when it's up again and will report it here when I get an answer.

I was intending to use the one on the back so I can bypass the amp and use it as a dac only for my home setup. But I thought the one on the back is balanced too... that's why I was confused with TRS and TRRS. I thought I'd need a TRRS on the back to get balanced because I'm not using their amp...

So I've ordered the iFi iDSD nano Black label for my new setup. And my old amp only accepts 2x XLR-3 ports as balanced input. Also if I'm not mistaken, the iFi iDSD nano BL will sound best with a 3.5mm TRRS jack. But I haven't seen 3.5mm TRRS to 2x XLR-3 anywhere. All I saw was only 3.5mm TRS...