Mixing front and center

For primarily music or movies?

If the former and for personal listening, those Dynaudio's should image like mad, and I'd wonder the need for a center.

If for group music listening or movies, you'd benefit with a center.  But I'd venture to guess with the driver differences between the two, you'd notice timbral differences across the front stage, especially when sources pan across.

I would sure try to match the brand and even series.  However, I ditched midfield surround for great two channel, and not only does the music sound way better with dedicated 2 channel replacing the AVR, but the videos sound, with excellent imaging, sounds better too. 

They are both nominal 4 ohms and both sensitivity 86 db, I wouldn’t pick such inefficient speakers myself, but starting with your FL and FR, on paper (I never heard them) that’s a very good center choice,

as it is very important to have similar responses at all volume levels, sometimes watching without sub-titles, and sometimes late at night keeping the volume lower and using sub-titles.

I had a small Bose center for many years, bought a cool looking but too efficient Klipsch center, just replaced it with a moderately efficient Jamo Center.

The Klipsch was too efficient for my dbx soundfield 100 mains, the Jamo much closer to their 90 db sensitivity, and I like the real cherry wood. I adjusted individual speakers within the AVR, but my recall was that the Bose blended better.

You need a center channel for content that automatically switches to 5.1 content, or you need to force 2 channel mode, which I often try, and find might sound better to me than some pseudo surround that somehow got involved.