Soma is a GABAa agonist of sorts, Lyrica mostly works by acting on calcium channels but can also shift your GABA:glutamate balance by acting on glutamate decarboxylase iirc, that is: in the favor of GABA.
There should not really be cross-tolerance since their direct effects are not related, but it is generally recommended against combining Soma with basically any depressant. For a depressant though pregabalin is not one of the more dangerous ones in such a combination, still.. particularly expect to get your motor skills extremely fucked up as well as other sedating/dizzying effects so I guess lie down for it. Also make sure that if you get sick you do it safely [no aspiration etc]. Respiratory depression may become a problem.
Personally I would never take the very high dosages of pregabalin with Soma that people sometimes take of pregabalin alone recreationally, a combo like this would have to be titrated and you may need a sitter but probably better if you don't do it..
I haven't had soma myself yet though I have an unheard of analogue of meprobamate and mebutamate, but am pretty wary of trying it.. in any case soma seems more reasonable with other combinations like hash.