Most commonly imported wild Discus are Browns or Heckels. They have really bad attitudes and a habit of killing our less aggressive and weaker domesticated Disucs. I'd strongly advise against mixing them, and if you do, the Domestic discus need to out-number the wilds by at least 2:1, and even then the wilds can absolutely hammer the domestics still...
Domestically bred Discus aren't fussy about water conditions, just so long as the pH is ABOVE 7.0 with imported Discus IME. Wilds will need a really low pH, below 6 ideally. The only way you can mix TB's and Wilds, is to get the TB's from a local breeder than raises his/her fry in really soft water with a low pH. Imported Discus will melt in the low pH water...
a 27g tank is far too small for anything other than a proven breeding pair. Put in two fish that are not a proven pair, and they will kill each-other. No if's, not buts, there isn't space for them to get away from each-other, and pairing does not happen until a heiachy is established and teritories set-up. Until this time, the dominant fish will bully the other into hiding and refuse to let them feed. In a larger tank, where there is more space, the subordinate fish will still be able to feed and keep away from trouble. This isn't possible in such a small tank.
Basically, you will kill some expencive Discus fish unless you buy a proven pair here. Sorry if this is blunt, but I feel the others that have been advising you may not have been giving you a fair over-view of your chances of putting a non-proven pair into your tank, so your information & opinions need balancing up a bit IMO