3 type S subs with 1 PPI 2150

First of all, you cannot create a 2-ohm load with a DVC 2-ohm sub.  This sub can only be wired at 1 ohm or at 4 ohms.  And no, you should not mix and match like this.  Let me see if I can explain it in laymens terms:  If you were able to wire one sub at 2 ohms on one channel of an amp and two subs to create a 2 ohm load on the ohter channel, the amp would not care, but the single sub will be utilizing all the output from one amplifier channel and therefor be twice as loud as the other side, where 2 subs are sharing the power.  Does this make sense?

All your subs should be the same for proper balance if you intend to run them off the same amp or at the same crossover point.