I agree on the the AVR being a really weak link.
But to further the discussion. Speakers are typically the first step in an upgrade cycle. If all components were matched and of equal quality, your speakers will make the biggest difference and set the tone and stage for your system. While your AVR may be the weak point. I would still recommend starting with speakers.
Audition as many as you can. The hardest thing early on is to be able to differentiate the source, preamp, amp, from the speakers. The only way to learn is to listen. You want to pick speakers that evoke an emotional response in you… they, sorry, speak to you. I remember searching for my first set of high end speakers. Really confusing… then a tears formed in my eyes… those are the ones I bought.
Get the very best speakers you can afford. Once you have your speakers… then start on the rest of your system. Break 9n your speakers for a couple hundred hours… listen to them, then more forward.