Not sure where you got that it "isn't rated for magnum calibers" since we list out a ton of them in the minimum barrel specs and the only place the word magnum appears on the spec page
https://thunderbeastarms.com/products/dominus-cb is this sentence, "Magnum and SBR rated". For the purpose of minimum barrel lengths, 7 PRC is basically the same as 7 RM, so 16" minimum barrel length.
Two other alternatives I'd suggest would be the Ultra 7 (same suppression as Dominus just lighter and 0.75" longer, smaller OD); or the Magnus, which will be much quieter than the Ultra 7/Dominus. The lightest option would be the Ultra 7 with a Ti DTHUB adapter.