Using codecs supported by phones, but not asterisk

i’d like to establish a session between 2 phones using codecs supported on both phones, but not supported on asterisk.
i tried various suggestions and combos thereof (canreinvite yes, dtmf sip info, no nat, media direct).
no luck yet.
seems to me (an others) that it should be doable though.
no problem getting all rtp traffic directly between the phones w/o asterisk in between ONLY IF
it’s a codec also supported by asterisk. i want to use codecs NOT supported by asterisk.
any suggestions?

i’m using asterisk 1.8.6 w/ freepbx, x-lite 4.5.5, snom300
i’m willing to try alternative freeware softphone since i’m told that xlite may not be handling
canreinvite properly (or at all).

As noted on your previous thread. Do not use any PABX at all. Configure the SIP URI of the paired phone in each phone.