I'm a beginner and just learning, so I don't know much.  I just bought two RME HDSP 9632 PCI cards.  I'm using Adobe Audition on a Dell desktop for studio recording and also a Dell rackmount for playback live gigs at jazz clubs.  I had major problems with recording latency, so the RME board seemed to be a good fit from what I've read.  I am recording a series of tracks from keyboards, bass, percussion, etc. in the studio.  I want to use the prerecorded jazz tracks/songs to play the guitar along with live at gigs.  The setup is basically a Dell rackmount computer, a RME HDSP 9632 card, an 8-channel analog output converter to 8 separate power amps and speakers for playback of all instrument tracks.  No premixed stereo sound system.  It's too karaoke sounding!  Just a speaker where the actual players would be.  Maybe a cardboard cutout of them!  Lol.  I want the sound of 8 channels sound system in the club to mix in the air like an actual band would sound.  I'm a one-man band and I'm also on the cheap.  I use a Behringer ADA-8000 for the analog output to the 8 speakers for the live gigs.  I use a second smaller system with 4 Klipsch powered speakers (total of 8 channels) as reference speakers for recording and mixdown in the studio.  Anyway, that's what I'm trying to get setup correctly. 
My question: While recording in the studio, I want to set up a pair of "quadraphonic" headphones (my wife wants more quiet time) to playback tracks while recording and listening.  I can mix the 8 recorded channels into 4 channels in Adobe Audition for playback through the 4 channel headphones while recording and building the songs.  How would I do that?  I don't want to have to physically disconnect the Klipsch monitor speakers to plug in the headphones into the back of the Behringer converter.  I have a Rane 6-channel headphone amp that I can use to separately power the 4 headphone speakers/drivers.   I also really don't want to use another Behringer with 8 analog outputs just for 4 headphone outputs.  Is there a breakout on the back of the HDSP9632 that I can solder together and make a special breakout cable?  Since the 4-channel headphone has 2 male stereo 1/4" musical input jacks, I need two female stereo jacks or 4 mono female jacks on a breakout cable (plus probably one stereo female headphone jack also, if possible).  I couldn't find a pin configuration for the RME card.  Or, do I need to get another separate converter for the headphones?  Thanks for any help!  I'm at a standstill.