piefon, I should say that I may be more sensitive to edginess - or lack of warmth - in cello sound than most. So, my opinion may be a minority one, and not significant. As to adding more warmth, though, there could be several factors, including, naturally, the cello itself and/or the strings. Certainly the microphone is a critical factor, as is the room where you record. But your engineer friend knows much more about these aspects than I do, I'm sure. Since you're a student working with (I assume) a very limited budget, I think you've made the best choice in keeping costs low by using your friend who's willing to provide his skills for a minimum of pay. I would say to keep doing what you're doing; concentrate on the music you want to transcribe for your duo and on making attractive arrangements of it. Most importantly, your recordings and playing sound professional (at least to me) and therefore should be taken seriously by anyone considering employing - or otherwise marketing - your duo. Best wishes!