I would suggest it is more about adjustments of the amps than a blanket "I didn't like them"...
When I purchased my first 300k in 1995, I have been using my Roland Cubes for ten years ...Immediately I noticed a difference, but tuning in the sound on the Yorkville, comparing to what I was use to..with the Cubes...I found the Yorkville a great, powerful unit...
When I purchased the Traynor K4 a few years ago...it took a bit longer to "warm" up to it..It never quite fulfilled my satisfaction compared to my Cubes (the standard I judge by).
Power and punch..no other combo amps match either the 300k or K4...
I checked out the 300k, for flatness with a scope...and the unit is near flat for 18 bands...almost a perfect reference monitor..
I think if you guys spent more time with the k4 and , Ian with the 300k..you would have found the magic of Yorkville..Also being use to your regular sound system...blocks your ability to hear..
Can you explain why arranger keyboard sounds "bad" in a sound system , compared to non arranger sound?....I bet it is the way you have your arranger tweaked for that inferior sound system you use..
...just kidding..well maybe a little bit