What platform is he using? Cubase? Logic? Pro Tools?
There are many preamp plugins, some do their job, some don't.
In my experience I liked what I heard with:
AM-Phibia by Magix
And LM-662 by Nomad Factory
Waves SSL Channel
But to get the optimum quality, your friend has to have a transparent frontend (soundcard & A/D converters) to his PC in order to keep the signal as close to original as possible (If your friend is plugging to his $50 soundcard, tell him not to bother
Even after that, some will say that the sound is not comparable to real gear, but with some creative tweaking, those plugins can save the day.
Hope this helps,