For several years I had a Model 1 and thought it was a wonderful amp, but I then auditioned a Pass Aleph 5 and suddenly the Rowland wasn't so satisfying. To some extent it's just a question of personal taste. The Rowland is a very good product, particularly at it's current used price (around $1,100). What you describe as instrumental tone I would describe as a coloration. For some types of music it's very, very positive and for others it's a slightly veiling of the sound. To the amp' s credit I never thought of this characteristic as amusical. By comparison the Pass offered a far clearer picture of the music with much less of a sonic signature. At the time I used the Model 1 with Monitor Audio Studio 20s, Rowland Coherence II (the original) and the Well Tempered TT.
I'm currently using a Rowland Concentra (version 1) and a Model 112. They are much less closed in sounding at the top than the Model 1 and are far less grainy, but at the same time they don't have the clarity of the Pass Aleph. I'd characterize them as richer sounding than the Pass, but they don't go so far that I would call it a coloration. Again, this type of characterization is heavily dependent on a person's sonic taste.
I'm currently using a Rowland Concentra (version 1) and a Model 112. They are much less closed in sounding at the top than the Model 1 and are far less grainy, but at the same time they don't have the clarity of the Pass Aleph. I'd characterize them as richer sounding than the Pass, but they don't go so far that I would call it a coloration. Again, this type of characterization is heavily dependent on a person's sonic taste.