Steve,
just saw this post. A particularly useful reference to Imperial German army bandsmen is the directory of military musicians published by Arthur Parrhysius;
Militär-Musiker-Adreßbuch für das Deutsche Reich. I am only aware of two editions - 1899 and 1913.
Interestingly GR 89 had two bands; one for I. and III. battalions (Mecklenburg-Schwerin) and II./GR 89 (Mecklenburg-Strelitz) had it's own band also. Consequently there were two bandmasters on the establishment of this regiment.
In 1913, the two gentlemen were:
Obermusikmeister Otto Frommann (I., III.)
Musikdirektor Hugo Hoffmann (II.)
The cypher, Schwerin or Strelitz will narrow it down to one or the other.
Obermusikmeister Max Vollmer of GR 110 had been that regiment's bandmaster since 1890 and was still in post in 1913 so he is the only candidate for that set of boards.
Regards
Glenn