Please don't write posts with extra spaces. It's irritating.

Second, you speak of the four speakers outdoors as not being real surround. Do you want surround outdoors, or just sound from indoors? Usually stereo sound from indoors is run outside.

If your amp has Speaker A and Speaker B, the way to set this up and work it is:
Speaker B wires to outdoor volume control.
From Volume control to speakers. ONE PAIR.
Since the outdoor speakers are stereo, you'll have to shut off surround and go to Stereo indoors so you'll get stereo outdoors. Otherwise your main sound (center) will be missing outdoors.

Now you can go outdoors and use the volume control to lower the volume in comparison to indoors.

Since you want to run four speakers, and outdoor speakers require more power than indoor speakers for the same volume, and you'll want to have the outdoor speakers in stereo, not in left and right of a surround setup --

all that says you need a separate two-channel amp that can drive four speakers. Take the Tape out or Rec out of your amp and send it to that amp. You then have to be sure you have analog audio connections from each source to the main amp -- digital inputs won't give you outputs at the Rec Out jack.

Volume controls are made to control one pair of 8 ohm speakers, but I've used them with two pairs of 8 ohm speakers with no problems.

Your approach of just sort of tapping off the main receiver, though, will be cumbersome or perhaps damage the amp.

If something is missing from this or the logic doesn't work, consider I'm taking a break on a job where we've worked fourteen days in a row. I hope I was sorta clear, at least.