Advice on Tonearm/ Cartridge combo

I've recently started using a SME 309 Arm on my SME rig, which is pretty low mass arm (9.5g).  The only cartridge I use and have is a Koetsu Black Goldline, which is a very low compliance cartridge around  (5 X 10-6cm).  I've been trying to make this combo work but these two just don't work well together, there's some resonance and distortion, especially with heavy piano chords.  Obviously I have change either the tonearm or cartridge.  Does it make more sense to get rid of the low compliance cart and get a more suitable cart to go with the SME arm, or should I trade in the arm for a heavier one that is more compatible with more carts.   

 Thanks,
J