Soundcraft Signature 12 MTK Output Level Help.....

Just replaced an older analogue Alto Desk with one of these afet hearing many good reviews.
Everything hooked up OK but the output levels seem really low compared to anything else I've used.
Even with Master on 100%, Channel 1 Gain at almost full (before clipping) using an SM58 mic my powered monitors (Focal Alpha 50's) are hardly being driven... The MST Meter LED's are showing good levels but the the output level just seems so low its unusable.
The Phones level is strong though...
Any clues as to if I'm doing anything wrong?
Cheeer
GJP