Not sure why you say the ARC is not balanced, the LS25 and VT100 is used to own definitely were.What I was saying is that although the ARC stuff is balanced, it does not support the balanced standard.
An example of how this is so is in a balanced line, the signal occurs with respect to its opposite, IOW the signal is the non-inverted and inverted aspects together, with ground being ignored. The ARC preamps do not ignore ground- each signal occurs with respect to ground rather than its opposite. The makes the preamp unable to control problems in the interconnect cable, meaning you have to audition the cable with the preamp, obviating some of the advantages of going balanced.