Fidelity of some amp-in-a-box distortion pedals

[Max]

Hi All,
I've built some of the effects from Runoffgroove that aim at reproducing one or the other famous amp sound, like the Azabache or the Ginger, and despite the sound being very nice, there's something missing.
As an example, take the use that Don Felder makes of muted notes in his solos with the Eagles, which according to him have been played through a Fender Champ at max. volume: if I try to play those muted notes, doesn't matter the amount of overdrive I get from the pedals, I never get that fat CHICK out of the guitar, it just doesn't seem to drive the effect hard enough, and of course it's reflected in the overall sound, the attack of the notes is different.
I'm currently using an Epi ES339, which of course is not an original Les Paul '59 like Felder's. Ah, I play through a cabinet sim (condor) and headphones, real amps are unfortunately out of question.
Anyone has any idea on how to tweak for example the Azabache to obtain that kind of sound, if possible at all? Or maybe it's a problem of my setup?