We have lived with both the LE Signature Series PLUS MK1 and a MK2 with APS R2 audio transformers and a pure copper inlet for almost a year now.
The sound very close. We like them both. The stock MK2 we did not think compared well with the LE SS Mk1. The modified MK1 sounded better.
With the upgrades on the MK2 it is very close with these differences.
The LE SS MK1 sounds more dynamic and live.
The MK2 sounds smoother and not quite as dynamic. More laid back but still detailed. This is with the new Blue Sky FW.