A few more questions ...
Is your receiver handling all of your multi-channel / digital sources?
How are you currently driving your wireless headphones?
Are you OK with completely separating your sources based on whether you want to run 2ch vs multi-channel?
In my case, I have a complete separation of analog and digital outputs ... I'm wondering if you could do the same, but your setup is a little more complex...
HTPC (HT Omega Halo) RCAs out to Saga input 1, set volume to max, select output source from control panel as necessary
HTPC Optical/Coax/HDMI (assuming on your mainboard) out to your receiver, select output source from control panel as necessary)
note: It's counter-intuitive, but you have to select "Stereo" under control panel properties in order for your receiver to process Pro-Logic from streaming video sources. Even set as stereo, your receiver will decode a DD/DTS signal if it's there.
Saga preamp out to your upcoming headphone amp.
Gaming rig HDMI out to your receiver via HDMI (optical does not support multi-channel PCM for gaming, its a PITA to be honest ... I have to reconfigure the HDMI to 5.1 for gaming, and then back to "stereo" to get my Onkyo to decode Pro-Logic sources in Sling / Netflix, and back ).
Blu-ray directly to your receiver, bypass the Saga completely.
Your upcoming headphone amp is your challenge. If you run it off your Saga, it'll be limited to your HTPC / analog source, and you won't get any of your digital sources (unless you throw a Bifrost / DAC in the mix), or unless the receiver is brought back into the mix. The Saga works well if you're completely isolating your analog and digital sources ... and have dedicated amps/hardware to play both. If you're trying to be more integrative with the Saga by using your receiver pre-amps / 2nd room outs ... I'd have to think on how that might work / what the implications would be.
Red arrows are 2ch analog connections
Blue arrows are HDMI digital / multichannel
For you, basically swap out my 2ch mini-tube amp with your headphone amp ... if I came close to understanding your usage.
Update: A Bifrost DAC would change this equation ... but I won't even go there yet ...