I'd recommend the Parasound zone gear, but they have limited inputs vs. outputs.
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Ebay has a few Crown CTS 8200 amps in the $400-600 price range. These are 8 channel amps and were very nice sound quality. That being said, they are going to be 13-15 years old. And they have a special connector for input signal (you’ll have to get the special plugs and wire them into the ends of the RCA/XLR cables). It is stable down to 4 ohms. I’m not sure that you are going to find a 8+ channel amp that is stable down to 2 ohms. These crown also have an internal fan that can get noisy if it is close to the listening area.
Finding 9 channels of quality audio for under $800 is going to be difficult to impossible. Ebay has tones of the "Niles Amplifier" 6-12 channel units within your price range.
Nord Acoustics makes up to 8 channel amps using Hypex NCore modules, but you are looking at $1600 plus.