When I got home I tried my infinity Beta 50's. They're not as rich and even sounded tinny to me.
your comparison isn't accurate, since the speakers you are comparing are in two different environments, the room adds or deducts to a speaker's overall sound.
three factors are messing with your comparison:
1) room acoustics
2) your acoustic memory is not accurate (the time going home is definitely a long time to wait to compare speakers)
3) in the store, you are straining to hear "new" stuff, that your mind tries to tell you that "yeah that's new" "and that too". (what you really need is an A/B comparison using a switcher or at the very least somebody switching it for you - without you knowing which is which)
you'd be surprised how much your mind makes up things with regards to audio, you think you hear something there, but when really really compared, the difference isn't really "NIGHT and DAY"
P.S. My source receiver is a Yamaha HRT-5960. Is this OK?
powering which pair of speakers? if it's the beta 50's, you need to set them to small and use a decent subwoofer.
in MY opinion, changing your sub will give you a bigger upgrade for less money. (you really need to get rid of that sub. the beta 50's might be capable of pumping more bass than that tiny woofer)
FYI, I have the Beta 50's as well, and Beta 10's, and Polk Audio Rti4's. and KEF Q1's, and have A/B'ed the Monitor Audio speakers (BR2 and RS1) with the ones I own.