The speakers you listed aren't much of an upgrade over what you have now.
You don't need towers in a room that size, especially if you already have a subwoofer.
The weakness of your system is the room first, then maybe the subwoofer, then the speakers.
I don't know what you mean by "more musical." That is too vague to mean anything except to reviewers who get paid to use words.
If you got the Yahama at a great price, maybe you can sell it for a profit?
There is no need to "upgrade" the Yamaha to an integrated amplifier. Who is giving you this (bad) advice?