You don't have to spend a fortune to get great sound, you just have to be methodical about your purchases.
Example: You have a large room and like to listen music or watch movies very loud, you're gonna need good subs to get the best perceived sound. Amplification is now very cheap per watt and with incredible measurements (ie, Hyoex, Pascal, & Purifi modules), so it shouldn't be a first consideration.
Untill you get *your* holy grail speakers, always be looking for speaker upgrades first, with exception to processors and sound formats/features you might need.