I combined DiPT with 2C-C yesterday. Unfortunately, my trip notes are appallingly lacking (nor was I collecting quantitative data on DiPT's auditory effects), so I doubt I'm going to write a trip report on it, but one specific aspect I want to note here, and ask if anyone's had similar experiences....
It seemed to me that c. 10 mg 2C-C, insufflated just after the peak of 120 mg DiPT oral (on a 16 hours empty stomach), produced an enhancement of DiPT's auditory effects beyond the peak they'd reached, as well as adding a little of its own 2C-C magic to the mix (in the form of moderate visuals, increased cognitive psychedelia and a sense of utter loveliness).
The problems with my interpretation of this as 2C-C amplifying DiPT are two-fold: (1) This being my first reliably weighed 120 mg dose of DiPT, I can't be sure that the DiPT-effects wouldn't have increased further anyway, i.e. that I misjudged the peak and it hadn't yet passed; and (2) the auditory effects notably affected were the closed-ear audials, and I'm not entirely sure that 2C-C can't produce those by itself.
Today I remembered Shulgin's view that 2C-D could increase or extend the effects of other psychedelics. I'm wondering (1) Has anyone noted this with 2C-C too; and (2) Is this in fact a general phenomenon with any psychedelic combination, that adding Y to X after the peak of X extends or enhances X's effects as well as adding those of Y? (Aside from 'shrooms/salvia, once, and some psychedelic/empathogen combinations, I don't think I've tried any psychedelics in combination before; so I lack the experience to answer these questions myself.)
ETA: On a separate note... this combo trip reconfirmed by newfound love of 2C-C. Its quality of loveliness (euphoric/empathic/mellow/playful) makes it, for me, suited both for recreational use and for serious tripping. The former, because feeling lovely is generally quite fun; and the latter, because feeling lovely makes me more willing to drop my guard enough to be able to explore the psychedelic state properly. I may be wrong that 2C-C consistently produces this loveliness, but it has done so three out of three times for me thus far (once oral 36mg, then oral 66mg + 10 mg insufflated booster, then this insufflated 10mg - actually I did another 10 mg about an hour later - with oral DiPT).
ETA: Actually, on reflection, I probably have enough memories of this to make a vaguely worthwhile brief trip report, so I'll do so some time soon, I expect.