I'd like to hear a bit more about why you think that is, if you don't mind. It does seem to me that Metzmacher might make some of the music sound less characterised than it is, but I don't have the othr recording to compare it to.
Ok, bearing in mind that I traded away most of the Metzmacher recordings a few years ago and my memory may not be as good as it is (also bearing in mind that I am not a professional musician nor do I have the scores at my fingertips right now):
Firstly, I think the recordings on the Wergo set (in particular Kubelik's) benefit from having the contrapuntal lines brought out more clearly--perhaps the drier acoustic has something to do with this--also they generally get more rhythmic punch into the music. Secondly, there's a sense in which Metzmacher doesn't drive the music as hard as he might: my personal view of Hartmann, particularly in the later symphonies, is that the Expressionist aspects have to be played up enough or the didactically contrapuntal dominates (this applies somewhat less to the earler symphonies, and my memory is that I found the recording of the 2nd the most successful of Metzmacher's).
I would choose the string quartets on CPO and the Gertler/Ancerl recording on SUPRAPHON of the Concerto Funebre.
I'd second those, with the proviso that the Zehetmair Quartet's ECM reading of the 1st quartet is superior (unfortunately they're yet to record the 2nd quartet). I also have some reservations about the
Concerto Funebre: the structure doesn't seem to me to quite hold together properly, though it's an immensely powerful work live. One other work I'd add is the
Gesangsszene, left incomplete at Hartmann's death, which inhabits a rather more stripped down musical world than the late symphonies and provides a tantalizing hint of what a late Hartmann style would be like: I think Metzmacher does a good job with this one (coupled with
Miserae and Dallapiccola's
Canti di liberazione).
I'm interested in a new recording on Capriccio of the
Sinfonia Tragica and Concerto for Violin, Piano and Orchestra: if anyone's heard it let me know.