Hey!
1. Well, I think doing a true clean AB test between 4.4mm and 3.5mm is a bit difficult unless you have the same exact cable in 4.4mm and 3.5mm terminations with same or similar impedance values because adapters add their own impedance (some adapters add more than normal amounts of it) and can change the clean direct 3.5mm sound a bit. I do have the same cable in different terminations but their impedance values have a difference of around 50 mΩ. I don't know if that contributed to the difference or not. Generally, more power from balanced out generally helps and benefits power hungry headphones and IEMs more than the regular ones. For example, Pola39 (likes power) EST driver treble sounds a bit fuller in the 4.4mm out. Overall, I felt that the 4.4mm has a slightly blacker background and in some IEMs a very slightly richer sound, though it wasn't consistent with all IEMs I tested it with. It also could be me imagining things. Haha
2. Well, only 3.5mm out is switchable between PO and LO. I'm sorry I didn't quite get you. Could you please specify what exactly you're wanting to know a difference between?
3. Well, I feel that DX160 is very neutral and portrays mids very naturally. Sorry, I don't find them forward or boosted above neutral.