I have a functional knowledge of live audio, but I've hit a wall while trying to help out my father in law. He does hypnotism sessions and uses an audio setup as follows:

Both he and the patient have headsets w/mics. These headsets have separate plugs for the earphones and for the mic. (they are this model here: Yamaha CM500 Headset with Built-In Microphone and more Consumer Headphones at GuitarCenter.com. (http://www.guitarcenter.com/Yamaha-CM500-Headset-with-Built-In-Microphone-103298519-i1126247.gc) )

He has a 4 channel mixer. Two of the inputs are used for their microphones. Another comes from his computer which he uses to play low music during the session.

The Tape-Out RCAs on the mixer are looped back into the computer so he can record the sessions.

The "Phones" jack on the mixer is hooked to the Client's headphone plug. The Client can hear him and themselves in their headset (sorta like a camera-comm system). The problem lies in trying to get my father in law's headphones to be able to monitor as well. The best I've been able to do is to get audio on one side of his headphones.

Is there such a thing has a splitter that lets you have full stereo in both headsets? (if I wanted to use the Phones jack on the mixer for example). Every splitter I've tried cuts out one side of his headphones. Also the tape-out seems to be a line-level and isn't adjustable, so if he plugs into that it's too soft for him to hear.

I've tried using the tape-out for his headset as well, but it doesn't have its own independent level adjustment like the headphone jack. I've also tried to have him jack into his computer but he said it was too quiet as well.

I'm wondering if it's partially because we have all these 1/8" plugs being used with adapters.

Thanks for any help!

Yes you can use a splitter but it must take into consideration the wiring of the headsets which may have four pin plugs rather than the more common three, if they do have three pin plugs then the headphones must be mono with the extra pin being used for the microphone.

One other option would be to get a headphone amplifier but this may not help if the wiring is special as highlighted above, either way you need to find out the wiring schedule for the headset mic combo and get the correct splitter to enable you to split the headphone feed but keep the mics independent.

P.S just had a look at the CM500 and it looks like it has two plugs, one for the headset and the other for the mic.

If that is so all you need is a 3 pin headphone splitter lead to enable both sets of headphones to be fed from the same source, I have one of these to do this with my camera: 3.5MM STEREO AUDIO JACK HEADPHONE SPLITTER LEAD CABLE | eBay (http://www.ebay.co.uk/itm/3-5MM-STEREO-AUDIO-JACK-HEADPHONE-SPLITTER-LEAD-CABLE-/370459077891?pt=UK_Computing_CablesConnectors_RL&hash=item564114ed03#ht_2371wt_1165)

It may also be that your mixer has 6.3mm jack out for the headphones so in that case you need one of these types: http://www.ebay.co.uk/itm/6-3mm-STEREO-Plug-2-x-3-5-Headphone-Sockets-Splitter-/320430498186?pt=UK_Computing_CablesConnectors_RL&hash=item4a9b25618a#ht_500wt_1180

If you do a search on the USA e-bay or go to radio shack they will be available there.