I went from a modified Magnepan 3.6r (rebuilt xovers, rewired new terminals etc) to Duetta sigs which I completely refurbished and brought up to 21 century standards.
If you go for it with the 3.6r and fix the xover and stands etc, you will have a hell of a speaker. But the Apogee if updated with the latest ribbons etc will be capable better dynamics and volume although even more critical of the electronics in front. I would say the 3.6 is a little more forgiving. My Duettas were sublime and a great speaker if powered correctly.
If you go for it with the 3.6r and fix the xover and stands etc, you will have a hell of a speaker. But the Apogee if updated with the latest ribbons etc will be capable better dynamics and volume although even more critical of the electronics in front. I would say the 3.6 is a little more forgiving. My Duettas were sublime and a great speaker if powered correctly.