Thanks for the insight...
To keep things simple I did not plan any line level crossover, it is simply the open baffle speaker that rolls off at 200Hz,
while the active woofers are connected at the line level to an LDR volume control and go up to 200Hz.
So yes, this way the bass still goes through the amp.
On the other hand, the original 8983 with only 30% mumetal laminations is rated at 5W.
Here is what Sowter told me regarding the custom full mumetal 8983:
"Thanks for your enquiry regarding the 8983. We’ve made some adjustments to the 8983 using our design program and are happy that an all-Mumetal core would be able to handle the 2W of your specification. We have had to make some alterations to the numbers of turns on the windings but this is purely to maintain signal levels as per the original 8983."
Some research also confirmed the lower Bs and higher permeability of the mumetal compared to permalloy.
The only thing I did not really find was a lower Hc of permalloy compared to mumetal, which would be in favor of permalloy.
Anyway, currently my gut feeling is to be adventurous and go with the Sowter...
Once the whole thing is completed, I plan to share some impressions and may be some pics.
But that will take some time...
Thanks
Fred