Hi... 

I have a stereo strings track I'm sending via the 7/8 headphone out on the UC to a summing box.

When I send any stereo track out via 7/8 on the UC with a special Y cable I purchased, the sound gets collapsed sounding, vs. the normal wide / expansive
like a normal stereo track does on any other set of RME outputs.

Here's the exact problem, visually: On the RME mixer software, the return channels from the summing box show that although 7/8 sends in stereo (with fluctuating L&R's), the return
comes back with both the L&R channels returning the exact same signals (No fluctuation / variation between both).

My question is, did I purchase the wrong Y cable to do this or am I doing something else wrong?

Here's what I purchased:

http://www.sweetwater.com/store/detail/YPP118/

This is what I think I should have purchased:

http://www.sweetwater.com/store/detail/YPP117/

Please let me know if I'm wrong or correct in my assumption...

Thanks!!