A D28 and a vocalist? Cutting bass too? And you've already got a Great River?
Definitely give the "Biz" a shot with that guitar, which as you've probably found is a VERY deep, rich instrument. The "Biz" will just give it a clear-as-day representation, making a somewhat cloudy sounding guitar come out just partly cloudy. (Fun side note for recording D28's: If you just put new strings on it...don't bother recording it. Play the shit out of it for like 5 days and THEN record it. True with this guitar moreso than many others I've had to play/record.) And if for some reason you're not using the Great River DI for bass, the "Biz" will slide into this role gracefully. The "dual" switch and cranked input can give you an amplifier-like texture.
The Vintage Design M581 will do the exact opposite of the "Biz" and is different enough from the Great River to not be redundant, so if you're into dissimilar gear, maybe tread these waters.
No idea when they're shipping, but there's a deadly piece of artillery called the Empirical Labs "Derresser" which is making the annoying parts of recording vox and acoustic guitar WAY less annoying. Indescribably natural de-essing and HF limiting which can take the spit out of a singer's mouth, and make string slide noise a thing of the past in about 2 seconds...and in a very non-offensive manner