High end AV receivers, worst investment in audio? Probably, if you buy new. Some people are OK with that. OTOH, I built my surround system using tube amps.
You don’t need an AVR (or pre-processor) to play multi-channel digital recordings (e.g., SACD, Blu-ray audio, and Blu-ray video). An Oppo universal player (e.g. UDP-205) will decode any digital recording. The Oppo UDP-205 has built-in "pre-amp" functionality, including selectable downmixing (e.g., 7.1, 5.1, 5.0, 2.1, 2.0), bass management (i.e., configurable subwoofer crossover), and volume control.
You can build a great surround sound system with two stereo amps and speakers (i.e., 4.0 or 4.1 system). If you’re interested in experimenting with this, I suggest that you conduct a test by connecting a stereo amp and speakers to the Surround Left and Surround Right and listen for how much content there is in your favorite recordings, and how much L vs. R distinction. Only you can decide if separate L&R rear channels are worthwhile. If L vs R distinction isn’t important to you for the rear channels, then combine the rear channel connections from the Blu-ray player into one via an RCA Y-cable. Connect one stereo amp for L&R, and a second stereo amp for center and rear.
I use the Oppo's analog line-level RCA connections to my vintage tube amps - in other words using the Oppo's DACs and pre-amp. (L, C, and R speakers are Klipsch RF-7II. The single rear speaker is an RF-7. Subwoofers: SVS SB16-Ultra, Klipsch R-115SW.)
Vintage tube amps generally hold their value, and sometimes appreciate in value. Vintage tube amps use discrete components that can be replaced, and therefore vintage tube amps can be kept running for many years. (I have 2 dozen vintage tube amps that are more than 50 years old.) And – most important – vintage tube amps generally sound better than AVRs IMO.
AVRs are “throw-away” technology. (I don’t think they make tweezers small enough to fix ICs.) If you’re OK with that, cool. All I’m saying is that for $5k you can buy enough “investment-quality” (aka “heirloom quality”) tube amps to power a surround sound system. You’ll just have to take a break during the summer due to the heat ...
I recognize that tubes aren’t for everyone. You can use two solid-state stereo amps to build a 4.0 or 4.1 system, as described above.
Is anyone else using two stereo amps to run 4.0 or 4.1?