I'm with you about it not being the injectors. There is a built in diagnostic test that lets you actually hear them working. Question: do you hear the pump whine when the key is first turned on? It should always do that because it building pressure to over 100 psi
which is reduced at the pressure regulator.
I've never heard of all the injectors going bad on an engine at the same time. I would want to make sure they weren't going to charge me for them if that wasn't the problem. With the Yamaha manual these checks aren't that difficult to do. Good luck.