I was jut about to buy the GR Servo Sub Kit 2 as well. So to be clear, you are sending the GR Kit 2 to Rythmic and Rythmic is going to use its sub box and install the GR Kit 2 in the box and send it back to you? Thank you.
If you want to build your own sub kit, go with the kit. If you want to purchase a completed sub, look at F12-G from Rythmik which appears to be the same as sub kit #2. In my case, I purchased a sub kit a while ago, with the intention of building the sub, but now I don't have access to a shop. I am going to purchase a stock sub, actually two of them, from Rythmik and they are going to discount the kit price to help out. I paid shipping to get the kit and then shipping to send the kit out, so not the most cost-effective but at least I don't have a kit laying around that I am not using.