While it may not be fully Balanced from Input to Output, the F1 certainly does have two Differential Line Driver chips, driving the 2.5mm TRRS Balanced Output. There are three different pin-compatible models of Line Driver chip that can be used in the F1. The socketed op-amp that drives the 3.5mm TRS Single-Ended Output, also feeds the input of the Line Drivers - so op-amp rolling is easy (except the battery obstructs taller devices). The Zishan DSD uses a pair of OP275 op-amps (soldered on the board) to drive its 2.5mm TRRS jack. It sounds good, but easy op-amp rolling requires adding sockets. Note: There are space restrictions in the DSD, as well.