So the malt bill is something like this?
- 65% Maris Otter
- 20% various Crystal malts
- 15% Aromatic Malt
...and you're not getting enough "malt" character from this beer?
I suppose the solution is dependent on the type of malt qualities you seek in the finished product. "Malt" character is as specific as saying you want "hop" aromatics; well, what kind of hop/malt character do you seek? Crackery, biscuity, bready, doughy, caramel, toffee, toasted bread, burnt toast, grainy, etc?
Nothing about your grain bill says that you shouldn't be getting plenty of malt qualities unless this is a really low abv beer, in which case it may just not be enough total grain to present itself in the finished beer. Assuming it's at least a standard strength or higher beer (5+%abv) then your grainbill is sufficient to get some biscuit, toast, and caramel/toffee(/raisin/plum) malt qualities depending on the types and amounts of crystal malts you used.
It is possible that you are using a yeast strain that is hampering your efforts, and that simply switching to a different strain that's more showcasing of malt qualities is enough to solve the problem. What yeast are you using? Some like 1056/us05/001/nottingham/etc can mask the malt qualities of the beer, whereas others like esb/1968/1272/1318 tend to help emphasize (or not mask) those characters.
Brewing process can play another factor in lost malt character but not one I'm willing to talk much about on this forum unless specifically requested.