Basement shower drain to toilet?? Some advice please before I JACKHAMMER!

The double wye would be vertical; in between the closet flange and the 90 deg. elbow. I was thinking of adding an AAV after the shower P trap as the shower will have a closet beside it; an inside closet wall can accommodate an access panel without it being visible, unless you think this is overkill.
I'm thinking the rough in should be further than 15 1/2" from the side as there is a cast iron rad there that your knee could brush against when your sitting on it. Gets pretty hot in the winter! I'll have to do a mock up in my bathroom and see.

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If you place the double WYE vertically it will be fine as long as you vent the shower trap seperately. I would suggest against the AVV (this has many names , pro vent, cheater vent etc....). If you can tie into an existing vent, it would be better.

Nobody will expect you to tear out the walls out of the next 2 floors in your bedrooms and kitchen just to pass a vent (like Mike Holmes does)
In this case, take the lesser of the 2 evils. Make sure you have future access to the AVV incsae it fails


Make allowances for you heating rad. 15" would be from your finished surfaces side to side (30"total min.) for what I like to call, elbow room.

Knee room is more important than elbow room in this case; The rads get awful hot when they're on full blast. It's such a small bathroom, though (5x7). I'll have to try and figure out the right balance.
Unfortunatly, I won't be able to tie in to an existing vent without going through the ceiling in to the other apartment. I don't think they'd appreciate it much. I think the jackhammering was enough!

Victory! Everything fit together and it works! Have a nice slope on the shower drain, plenty of room for the kerdi drain on top. I was able to tie in the copper vent with my 3x2 double wye without too much difficulty. I ended up having to drive to vaughan for the double wye as Nuroc was out of stock. Very helpful, though. Picked up the AAV there. $50! Probably cheaper if you have an account.
Funny thing; Was at HD after picking up the AAV at Nuroc. The shoemaker working in the plumbing department was telling someone to use the $3 abs version for their basement. Says right on it for mobile home/rv use only. Glad I asked here instead of there!
Thank you very much for your help!

I'm glad I could help Delta_v