About 2600 sound.
The console is so large because it was to have 2 stereo speakers in the console.
That got scraped, and they combined the left and right channels and sent it out through the RF TV signal.
USA NTSC TIA Pin 12 and 13 have the 2 sound channels.
If you pull the signal from those pins, each through a 10uF capacitor to the connector, then the connector to ground, you'll get what they call "2-channel mono".
[ Pin 12 to 10uF ceramic, or "-" of 10uF electrolytic capacitor, to RCA white (left) connector (center), then the outer (barrel) RCA to any ground point. ]
[ Pin 13 to 10uF ceramic, or "-" of 10uF electrolytic capacitor, to RCA red (right) connector (center), then the outer barrel RCA to any ground point. ]
The early games, like Combat, were programmed taking these 2 channels into account.
For instance, the tank on the right will come out the right speaker, the tank on the left will come out the left speaker.
There's no logic when both players cross to the other side, however. The original right tank audio will still come out the right speaker, even if it's all the way on the left side.
SpeceWare's remake of Warlords called "Medieval Mayhem" uses this stereo effect. Hits on screen right come out the right speaker, hits on the left come out the left speaker. And the intermission when the winning Knight makes his walk across the screen waving his colored flag, the audio follows (I think).
I hope "Medieval Mayhem" is one of the titles you purchased from the AtariAge store. It's like comparing "Asteroids" to "SpaceRocks". That much improved.
And "Star Castle Arcade" is another one that is near arcade accurate.
There was a programmer who made an 8K version, to show to himself it could have been done, and not turned into Yars' Revenge (which was to to be Star Castle).
When asked about sharing or purchasing his version, he declined, but with urging he finally settled on $32,768, which is when I suggested we make a great version.
A few months later we HAD a great version shaping up. So programmer 8K decides to do a Kickstarter. He managed to get 418 people to pledge $23,946 and still had to manufacture 375 carts, boxes, stickers, LED's (yes the cart lights up during explosions), instructions, and mailing.
Some people find regular gaming with the 2-channel audio split to be annoying.
You can use a Y-cable or a simple mixing board to combine the 2 separated channels back into 1 mono channel and send it to both speakers.