In my experience, the effect the horn has on the sound is way down at the bottom of the list. Most of the sound comes from the player, then the mouthpiece/reed, then the neck and finally the horn. If you want a different sound, try to copy those who already have that sound. Then experiment with mouthpieces/reeds. Changing horns will have virtually no effect because you will automatically compensate for the differences and end up sounding essentially the same, whether you intend to or not. Just listen to any great player on several different horns. The differences are miniscule.
As far as subtone goes, with practice you can get a great subtone on any horn.
I've been playing a really long time but have only been on forums like this a very short time. One trend I've noticed in this short time is that beginners love to collect horns far more than they want to practice, refusing to accept the fact that the horn doesn't really matter very much, so long as it's in working order. I know you practice a lot. But to improve, it has to be very focused practice. If you want to improve your subtone, practice subtone A LOT and listen to subtone a lot and experiment with your embouchure a lot. Start on a note you can easily subtone, then slowly work your way down the horn. Repeat until you can't make a mistake.
Example of how the horn makes little difference. Listen to Jay play an American vintage horn vs. French vs. Japanese. Yes, you can hear tiny differences, but there's no way I'd be able to tell which is which just by listening.
In this article I discuss and compare these two saxophones and try to find out if the Yanagisawa can replace my Mark VI as my main horn.
bettersax.com