This may seem like a crazy idea. How about just build yourself and open baffle center channel using the same midrange driver and tweeter used in the Europas? Or just grab a decent wide range driver or two and do the same thing.
I know the midrange driver used in the Europa is a Aura Sound NS6-255-4A 50W @ 4ohms. You'll probably spend less than $150 on the whole project. The midrange driver will run you $40.00. It's frequency response is 56 Hz to 7 kHz.
The tweeter is a Morel. Not sure of the model number. With a resistor or two, capacitor and one inductor. You could come pretty close to matching your mains. The center channel is mainly for dialog any way.
Better yet how about just use one or two of Aura sounds fullrange drivers in a open baffle? They should cover most of the frequency a center channel needs.
You can get the Aura Sound NS4-194-4A
wide range drivers for $14.35 a piece.
Frequency response is from 72 Hz to 18 kHz. These drivers are super efficient. 10 wpc is the most this driver needs.
You could use resistors to pad them down or go with a less efficient wide range driver.
There are others. Here you can check them out for yourself AuraSound
Here's a place to buy them SOLEN of Canada
. Click on the link at the bottom to check prices on this page.