SE846 are more sensitive, need lower volume, and you used it with single ended 3.5mm lower power output of RU7. Switching to more demanding IEMs and balanced output that draws more power forces you to deal with iPhone limitation that caps how much current external devices can draw from its lightning connector port. The same setup will have no issues using Windows, MacBook, iPad, or any Android devices because none of them have current limitation. But iPhone does
Scroll toward the end of this page in my RU7
review, I covered it there. You can reduce power draw by switching RU7 to DSD64 oversampling, down from DSD256 or DSD128. You can switch to some ddhifi usb-c otg cables or even an adapter to brining in external power, or maybe you can get 4.4mm to 3.5mm cable plug adapter so you can go back to single ended output of RU7.