If you're lacking in power - that Roskan is 120W per channel - then you need to double up the power. 3.2 max power handling is 300W.
Peak SPL Calculator
120W should be plenty. What makes you think you're lacking in power? Or perhaps PSU not capable? You said you have been using 4 channels to bi-amp the Kef's that should be more than enough.
With your amp you should get 105dB or thereabouts
You could try using bass management, say small 40hz or small 60hz, that will free up some power.
Affordable 200W amplifiers are Rotel but I found them a bit clouded. Audiolab are brighter and good match for the Kef's.
My other speakers (Celestion A3) are also 4 ohm, so both Kef and Celestion need a amp with a decent power supply.
I'm using a Outlaw ICBM1 between pre and power and that helps, and easier to integrate subwoofer. Perhaps try and find one of these? For whatever reason you think you need more power, you could try the speakers on small 120hz, and therefore free up power and determine if it sounds better, or high passing makes no difference, then work out if amp is up to the job, or not.
Oh have you tried the Kef Room compensation device? (inside the speaker terminals) That won't free up power, however if it's too bassy you can adjust it.