Not that I don't like the MC90 in it, but I am curious. I have a Thiele and I might swap speakers to see how it is. OH, that extra weight though. :lol:
I put one in my Mk V, and suddenly the Mk I, II, and IV modes started sounding like the Boogies that I'm used to. Due to the magnet size, I had to mount the speaker from the front (The grille hit on the speaker, so I had to use 1/2" spacers and longer screws to secure the grille properly)
The downside is the added weight, but the tone is WELL worth it!! Good luck!!