If you are serious about buying for the long term, then I think you are going about it the wrong way.
Establish what level/quality of sound you like and then figure out what it costs. If you figure out whatever you like is over your budget right now, you have a decision to make: save up to buy what you want (up your budget), buy used (if you can within your budget, revisit the objective of buying for the long term.
Don't buy a receiver until you know what speakers you want. The 663 is a great budget receiver, but may not drive some speakers (4ohm load).
Don't ditch Klipsch (he, that rhymes

) because of what you read, ditch them because you don't like them. There is significant variation in what people like.
[/start rant] If you read what the guru of preceptual research, Dr. Toole has written, you will note that he writes that
once properly trained people overwhelmingly prefer a speaker with a flat frequency response (slightly rolled off on the high end). Read the part in bold. Read it again and think about what it implies and how that fits with what people post here day after day. [/end rant]
I feel better now.
If you read through posts here, you will see a number of speakers recommended over and over again. Trust your ears. Good luck with your search.