I'm not an expert with terra cotta/saltillo but it would seem to me that having topical coatings leaves the possibility of being scuffed up - leaving those whitish lines.  I have no experience with TK6 - and it sounds very tough, so maybe that's not an issue.  I've certainly seen many topical coatings being open to that possibility though.

We have had some good success using Aldon Chemical products and finishing with S-B-S solvent based penetrating sealer which has little gloss to it.  What you use may depend on any existing coatings or sealers.  Just another option you may want to explore.

Stuart Young
Santa Fe Floor Care