The difference in the two is the IX is a incross so most likely the seeds you have are f1 x f2 and it could be both ways in which parent is f1 or f2. Your seed are pure Tresdawg just not a single generation but a incross of multiple generations. A BX is a backcross usually a pheno outcrossed to something and then a male taken from that cross and hit back to the original mom but you can also have a BX of the dad also and that's basically what Tre Stardawg is Stardawg(Chem 4 x Tresdawg) x Tresdawg
If you have any plans to grow those soon please make f1 of it and think of me
those and the Guava 13