I tried both the K4 and 300K and found both unsatisfactory for arranger use. Now, this is strictly my own personal opinion. I have tried a K4 with both a Roland GW-8 and a Yamaha PSR-S900 and I was not impressed. Several years ago, I tried a 300K with a PSR-8000 and a Roland E-series (a 600 I think) and felt the same way.

However, these exceptionally well made and very powerful units are ideal for amplifying electric pianos, synthesizers and clone-wheels(the latter's rotary sim benefiting greatly from the stereo feature) and I have used a 300K for playing in a band for several years with excellent reliability and lots of punch.

They are combo amps and designed as a keyboard monitor for the keyboardist in a band.

Using with an arranger, I found they weren't as good as two seperate powered speakers in stereo, or a stereo power amp with two speakers.

Try before you buy, is my recommendation.

Ian