...forthcoming from DaCapo:
http://www.mdt.co.uk/helsted-decet-and-string-quartet-randers-kammerorkester-david-riddell-dacapo.html (http://www.mdt.co.uk/helsted-decet-and-string-quartet-randers-kammerorkester-david-riddell-dacapo.html)
Out of 5 string quartets, three of them numbered, Da Capo have chosen the last, unnumbered string quartet Op.33 in F minor. This happens to be the only one with parts available on imslp, plus a slightly chaotic rendition which plays 2 minutes shorter than the new recording (this is what I was hoping would happen, and I don't mind conceding "premiere recording" status!). The date (1922) and style are perhaps a bit modern for this forum.
I just registered that in the new recording the string quartet is apparently played on string orchestra. I can see how that might work pretty well (and why some tempi are on the slow side) but we still need an authentic premiere recording!
It's the earlier (1891) Decet that I'm primarily interested in...
There's a (freely-with-conditions etc) downloadable score-or-parts of the Decet (will check when I'm back later, in a rush now) at the Danish Library, see OCLC Reference here (http://www.worldcat.org/title/decet-for-fljte-obo-clarinet-fagot-horn-2-violiner-viola-violoncel-og-contrabas-op-18-komp-1891/oclc/871308559).
Audio samples are now available here:
http://www.dacapo-records.dk/en/recording-gustav-helsted-decet--string-quartet-in-f-minor.aspx (http://www.dacapo-records.dk/en/recording-gustav-helsted-decet--string-quartet-in-f-minor.aspx)
Absolutely nothing to frighten the horses there. BTW the String Quartet was probably written in 1917.
I should have said, manuscript score and parts of the Decet are also on imslp, possibly from the same source that Eric has located. The score looks like it could be the composer's autograph (i.e. barely legible) but the parts are in an exceptionally clear copyist's hand.