Thanks Dan, hope you are well and stay that way!!!Hi Mark, sorry for the late reply.
I was in the hospital for a couple of days and was just released today.
Yes, BMW OE speakers are 2 ohms and the Focal are 4 ohms.
The OE BMW amp is powerful enough to drive a 4 ohm speaker without any problem and there is no noticeable mismatch on speaker output either.
So in summary yes, the Focal is a very good replacement for the stock center channel speaker and the BMW amp has enough power to drive it.
It is funny how the revival of this thread spurs new interest in this upgrade. I posted my change to focal on my home board for the 6 Series and had 6 people who wanted my spare speaker, ended up putting some folks together who bought a pair to split. Anyway, your DIY's always are relevant no matter how old they are.
To the guys who are considering this, search out Dan's (whatheheck) post on changing the tweeters over to Polk Audio. That to me was a GREAT upgrade, even more noticeable than the Focal center channel.