Welcome to forum svrider.
This should teach you never to listen to what other ppl say.
You should pick a pair that you could actually listen to before purchasing.Anyway,enough "salt in the wound".The amp you have,Yamaha,is not the smoothest one around and in combination with the Triangles(French loudspeakers=overbright) screwed things up.If your Yanaha had pre outs,maybe,just maybe with the right tube power amp and interconnects/speaker cables things would mellow up but i seriously doubt it.If you don't like that particular kind of sound,those "addition" are only meant to make it better but only in THAT direction if you understand what i am trying to say.Basically,the sound will be the same,just better.To be honest with you,i can't see how you can integrate a power amp or pre/power or integrated with your existing home theater since without spending a small fortune
,since your Yamaha don't have pre outs not to mention that you will get into the "upgrade" thing wether you like it or not.IMHO,sell the Triangles,use the cash you are going to pay for the tube amps together with the money you'll get from the Triangles and get a new pair of loudspeakers that will be more to your liking and musical tastes.
I am really sorry if i was too forward with my reply but this is the bitter trouth.

It's probably a safe bet to say there are likely a host of speakers in the $1K - $2K range (new & used) that may better cater to your musical taste and sonic preferences.

You can try to "tweak" the sound with different components upstream in the chain or you can try different speakers and see how they integrate with your system and your tastes.

Good luck!