I own an Envoy and I like it pretty well. It is well built and reliable and my dealer has provided outstanding after sale support. The D1 is also an excellent choice from what I know. Here is the thing. No matter which one of these you buy you will quickly learn how to optimize it for your use. You do this by moving around, side to side, up and down and so forth to hit the areas of your body that you want. Any good spa will provide optimal hydro message if the user learns how to use the thing. The other thing is that our bodies change and our needs for message change all the time. At times the Motomessage hits the spot for me, but other times I like the two corner seats better. For my shoulders and neck, the Moto thing is not so great, just as you describe, but the middle seat between the two corners really gets the job done for me if I just squinch down to where my head is barely above water level. Wow, I am ready to hit the tub just thinking about it. The foot jets on the Envoy are strong, the calf jets are useless for me. If I need to hit the calves, I sit in the well and turn to get them in front of the foot jets. Again, you need to experiment.
Were I you, I would choose between these two on the basis of the dealer. Which one do you feel more comfortable with? Which one is closer to your home? Ask to speak to the service guy. How long have they been in business? Ask for a few happy customer references. Find out if there have been any complaints about them with the BBB, the chamber of commerce, or state attorney.
Let us know, how it goes.