Machine emb. on T shirts is not difficult. Hoop a stabiliser like a "no show mesh" type. Spray with 505 basting spray. Stick your T shirt to the stabiliser and embroider away. I have a Janome 300E.
I use Madeira rayon thread, or several types of polyester. I've heard NOT to use Janome thread.
I use Schmetz universal needles.
What's not working?
I'd love to be able to help you. You're NOT alone!

Also, try the same design on some nice stable cotton before you try on a t shirt. Feel free to adjust the tension.