Hi Gabriel and everybody on here!
My name is Brian, and I am the Vice President of Sales and Marketing for Praxis Musical, as well as the Product Specialist. Praxis Musical is the manufacturer of Sterling By Music Man products, which includes the new SUB Series.
Gabriel: The strings that the SUB Series comes with from the factory are generic, Asian made strings. Not the best in the world, but, for us to reach the price point that these sell for, those are what we had to work with.
Of course, we always recommend that you use Ernie Ball strings as replacements.
On the Ray4, I'd recommend using the EB2832 Regular Slinky.
On the Ray5, I'd recommend using the EB2836 Regular Slinky 5 String.
I hope this helps, and if any of you have questions about the SUB Series or Sterling By Music Man models, I'll do my best to answer your questions!