I've compared the original master with a LD2 - but not the 2+.
Heres the surprising thing - I couldn't tell the difference! No discernable sonic difference between the 2 amps, if I was blindfolded and volumes matched no way could I tell the diff. Using HD650s also had a listen through HD595s.
Honestly, if you want to experiment with tubes, get the LD2+, know that you will have to replace the tubes at some stage, buy an extra set when purchasing the amp. Know also that some LD2+ have given problems, but that these were fixed by the maker quickly and to owners satisfaction.
If you want a simple fit and forget solution then get the master. Sounds poor until it warms up for an hour or so. A friend has one and is very happy with it, only thing is that one of the RCA inputs came a bit loose. Comes with a separate PSU.
both give quality sound its down to tubes/SS!
Fran