I had a hard time with acoustic from the DT but I came up with a solution that seems to work well. This patch works amazing with my DT25 head, 2X12 sealed cab with Celestion V30s and it should work fine with any other DT setup. It may not be perfect but it works with all 5 acoustic models.
I put a flip top in channel A, centered the mixers and then mute channel A. You can use any amp model in channel A, it is just a placeholder. I use it for low DSP. We are not running through the flip top at all. We are only using it to "lock" the DT from switching to the amp in channel B and to control the physical topology. By placing no amp in channel B and muting channel A in the POD we effectively send the clean "unamped" acoustic guitar signal straight to the DT power section through channel B! I set the topology to III in HDEdit and it just gets that nice sort of resonance you would expect from an acoustic. We also have to change the input to Variax-Same to ensure that our signal is passed to channel B. You may have to turn up the mixer levels for volume matching and add an EQ for tone shaping. I use a reverb in the chain too.
I also use this setup for synth tones through the DT. Place all your synth and FX blocks in the B path or the post mixer and you will get the pure synth without the amp coloring just like with a FRFR solution.
Here is a link to a set list with a couple of variations of this concept... try it out and give me some feedback if you like the idea or not...