I like it! The instrumental, as well as the vocals, sound really fun!
I don't know if I agree about the vocals drowning out the instrumental--I mean, I guess they might, but I think it's important that the vocals can be heard/understood. You could probably make an argument either way, depending on what effect you want to achieve. If there's more that you want to be heard from the instrumental that you think isn't coming through, you could adjust the volume on them up some, but I don't think it's necessarily imperative.
Potentially, I think you could turn the volume on everything up some (which would probably help with hearing the instrumentals too, of course), but that's completely dependent on the person listening and what their volume setting is--it's just that I was listening to some other things and this song came out quieter than them. So it might not be a valid point. To a certain extent, I'd guess it's better to err on the side of being too loud than being too quiet, since whatever people are listening on, they can always set the volume to 0, but the max they have available could be different, and it sucks when you need something louder but can't get it there.
If you turn up the volume on everything, I think you might find that you want to turn down the volume on Rin, which would sort of incorporate the feedback from the others, too.