The ornamental design for a musical instrumentstandassembly, as shown and described.
1. Musical instrument stand assembly
1.1 is a front perspective view.
1.2 is a right perspective view.
1.3 is a right perspective view shown in an alternate lowered position, using the alternative discs for a wider bell.
1.4 is an enlarged fragmentary right perspective showing the tube holder with the tubes attached.
1.5 is a perspective view shown unassembled with the alternative discs.
1.6 is a perspective view shown in a collapsed configuration with the alternative discs.
The musical instrument stand assembly includes the collective appearance of the assembly of its components which can be reconfigured to fit any size bell of (bass) trombones, alto horns, euphoniums and similar musical instruments by adjusting and/or exchanging the rings.