Sev are you still there reading this?
The balance issue between crossbows and melee is that meele attacks almost 3 times as much in the same amount of time. Adding 1 extra crit multi (when compared to other trees thats all it is) will in NO WAY close the gap on the damage of meele, especially when augment/thunderforge procs hit so hard and so much more often. You either need to add a massive amount of doubleshot to crossbows to make them viable (as I dont see how you could possibly increase the speed enough unless you get rid of reloading entirely), or we can go another route!
Why dont we try something unique here= Crossbows are slow but deal MASSIVE damage.
The way you could do this easily is=
Increase ranged attack power by 100 when a great crossbow or regular crossbow is equipped (slow but hits like a truck!)
Increase ranged attack power by 25 when a repeating crossbow is equipped. (fast with a needed added damage boost to catch up to manyshot/10k stars)