Just as a gratuitous bump, I believe people say that the 340 gives you some more bang for buck in the HT sense, but that the Sierras are the wtg for critical music listening, granted that you have the money. The latter may or may not appreciate a better amp section, but I cannot recall the opinions of owners right now.
The 340s have dual woofers, are significantly larger, and have a rough sensitivity of 90-92db/w/m, whereas the Sierras are 86.5 (which is on the low side for sure, I think of Totem or certain Aperions with that #).
I'm sure you'll be happy either way. cheers.