I don't consider myself an expert but I'll answer anyway
I personally think you should have a great sound now; name brand audio interface and active studio monitors. You didn't say how many channels you are running, is there a subwoofer and what sample sets you are using.
Quick comments on your current setup:
Forcusrite receives a lot of accolades for their pre-amp design and British EQ quality for studio sound. This means nothing with regards to HW since we are focused on the outputs (digital to analog). Regardless, the few setups I've heard with the Scarlett series have sounded good.
The
Behringer 2031A is an excellent active monitor for Hauptwerk. Simply search for "2031A" on this forum or look at pictures of various Hauptwerk installs for confirmation. Professional and other user reviews confirm its 'wider than normal' sound field and a focus on midrange frequencies, both of which are perfect for pipe organ simulation!
Adding a decent active subwoofer would be a noticeable improvement.
The new crop of MOTU interfaces which includes the 24Ai and 24Ao models, say the sound rivals that of interfaces which costs twice as much (RME for example). Other brands of studio monitors around the 2031A price range you start to get into a personal preference decision. I doubt monitors costing a $100 more will give you $100 worth of better sound.
Without knowing more details of your current setup, my advice to enhance your sound would be to simply add more 2031A monitors and move into the multichannel arena. Spreading a chorus of pipe ranks across multiple speakers is thrilling and a definite upgrade. I currently have 8 Behringer 2031A monitors and every time I've added the next pair, I noticed an enhancement! There are several sample sets that are surround sound sets which use 4 to 6 separate channels. This takes it to the next step to simulate the cathedral or venue the pipe recordings were made. Now that's an upgrade!
Danny B.