After you've extracted the files from both the model and voicepack, you should be able to just copy the voice portion from the voicepack UPL file (e.g. Voice=HomerJay3.HomerJay3), and paste it into the model's UPL...so it'll look something like this (single line):
Player=(DefaultName="Homer",Mesh=HomerAnim.Homer,species=xGame.SPECIES_Jugg,BodySkin=Homer.HomerSkin,
FaceSkin=Homer.HomBod,Portrait=Homer.HomerIcon,Voice=HomerJay3.HomerJay3,Text=XPlayers.Homie,Sex=male,
Menu="SP",Aggressiveness=+0.5,CombatStyle=+0.6,FavoriteWeapon=xWeapons.RocketLauncher,Ragdoll=Male)
Then delete the voicepack UPL so you don't end up with two characters using the same voicepack. The game will grab the taunts from HomerJay3.u, and use the other sounds (grunts and hits) from the juggernaut. If you want to change those other sounds, then change the species/sex of your model. The species names are all found in xplayersL1.upl. I changed the species of Spawn to night male, though sometimes it seems to revert back to juggernaut....maybe there's some hard-coded audio tied to the juggernaut model.
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/ >) My 84-year-old non-techy mom uses Debian Linux. It ain't that hard.