You should have a good listen to the stage when it's quiet and see if there are any strange echos or booms etc
I would guess that bass trapping would help fix your problem, seeing as you say the sound is muddy and unclear. From the little I know about it muddiness tends to come from excessive bass reverb in the room ( often masked by mid/top reverb ) .... the vast majority of concert halls and recording studios pay great attention to bass trapping as it's one of the single most dominant causes of bad sound. This is probably all over the larger room not just on the stage but it depends and there are others far more expert than me in this field.
The good thing is that its fairly easy to diagnose, but you need some materials, which are by definition bulky. Just get lots of sound deadening material and put it in and around the stage ( corners are best ) and see if it improves things, if it does you can do the same thing except on a more permanent basis.
I say around the stage as you probably have no option on the rest of the room but really it's probably a room problem not a stage problem though I think any dense absorption in any part of the room will absorb the bass reverb even if it's in another part ( but I could be wrong on this )
Sound deadening material ( for bass ) must me very heavy, dense and thick. A big couch for example, or a stack of mattresses or something. The more you have the better ... in fact it might take a lot more than you realise to get an effect, ( and if there are hard walls and floor you need a heap) which is why you can get strategic with it by placing your bass traps at node points ( which I'm sorry to say I don't know how to calculate but if you google johnlslayer or ethanwiter then you will find lots more ) .... the no 1 strategy thought is to trap the corners ( remembering corners in the roof and floor lines if you can use them )
for instance a nice ad hoc bass trap would be to stack several rolls of rockwool ( which is perfect for this ) on top of one another in each corner right up to the ceiling, making them safe of course. You can drape fabic over them if you want but that's it you don't unroll them or take them out of the plastic or anything.
It's a job you get done by degrees and try to spend as little as possible as much of the materials will be available from non pro sources - of course you can get professional treatment kits and ethan winner actually sells several pro bass traps too.
Check also for any strange flutter reverbs or anything else that you can reduce with strategically placing sound deadening material around ( remember you need depth of material to get low frequencies which are normally the issue; and thin materials will get the top and mids which you normally want to leave present unless they're part of a flutter or something or unless you want a totally dead room, which isn't ideal. You can google RT60 time for your particular type of music to find more on that one.