Time to upgrade DACs

First, what type of improvements are you looking for over what you have now, and what sound characteristics of system performance overall are most important to you?  Without that info this is all just a crapshoot. Also, the Sonus GPs are good speakers but radically different in design and sound from the Moab. What has pointed you in that direction?

I am looking for a bigger-fuller sound with really good imaging. I have heard a lot of good things about the Moabs on this forum and elsewhere, but have not heard them.
So your correct it would be a bit of a crap-shoot... Not sure what to do but got the "upgrade bug".

I dragged home the Marantz HD DAC1 and thought it was nice. Not knowing your speakers I would agree it might make sense to sell them off with the subs, take that money along with the $2500 and visit speakers. No doubt a better DAC may get you what you’re looking for but speakers may get you more of it for less. I recall the Marantz has a nice full, warm analog presentation so I question it’s the component to address first.

I’m sure your SF are no slouches either for the money but no doubt differences between DACs can be splitting hairs but I’ve never compared speakers with each other and couldn’t hear the difference immediately. 

Rather than solve the dilemma, speakers or DAC, let me suggest a 2-300$ alternative: a super re-energizer & reclocker like the one I use. (Fantastic little device, kudos to my dealer!) You should expect a fuller sound with better hi & low-end extension from your current DAC

The reclocker lives between the source and the dac and cleans USB noise, energy, & phase issues. -
In fact, I now daisy-chained two 3Rs and gave up on replacing the DAC (for now).

Check the improvement such a device makes and decide if you still want to change the DAC. Even if you spring for a new DAC you will still keep the reclocker -- it is useful even on a 100k MSB (I tried my 3R on one). Regards

As others have mentioned, swapping the DAC isn't going to get you 'bigger, fuller sound'. Having said that, I'd consider the RME ADI-2 FS as a DAC because it has a 'loudness' feature that may provide the bass you're looking for at lower volume levels.

The SF speakers are probably the weak link in your chain. I had a single REL T7 and was pretty happy with its performance. If anything, I'd expect dual T9i's to fill in the low end pretty well.

Based on your desire to add 'fullness' and good imaging, what you probably want is a tube preamp. Tubes will add warmth (fullness) and increase the image size. However, images may be more vague with less pinpoint accuracy than an all solid state signal chain can provide.

In regards to imaging, perhaps consider speakers with ribbon tweeters. IMHO good ribbons image far better than any dome tweeters I've heard.

Also, is it simply a lack of bass that you're missing or does your current setup simply lack warmth? What setup were you running in the past that makes you think your current system lacks fullness? Could it be your current system is simply more honest than what you were previously used to an you actually prefer a system that shelves the high frequencies?