I have to admit I had never heard of Eugen Suchon before encountering this stamp. Born in 1908 his father was an organist. His early piano studies led to further training school. He studied in Bratislava and Prague. He has a nicely rounded oeuvre including music for a wide variety of instruments, voices and combinations. A psalm cantata and a folk-song -based opera sealed his place as a Slovak composer of considerable import.
The present stamp features an image of the composer, an organ facade, the composer's name and signature. The organ may be that in the Reduta concert hall, home of the Slovak Philharmonic orchestra. The image I found on the orchestra's site is rather distant, but one can discern the medallion on the facade, which seems to correspond to that pictured on the stamp.
Suchon's connection to the organ seem solid if somewhat slim. His father was an organist. As a composer, there seem to be three larger-scale works for organ, all with orchestra.
This stamp (Scott 539) was issued in 2008, to honor the 100th anniversary of the composer's birth.