Yes, @Ant to replace your OB bass and reach your mid horn, you will actually need 2 horns with a steep slope between them. Will be hugely complicated to implement and need serious real estate. Been there. 
Worth it though, if you can swallow the pain.
Another way could be a mid- bass horn and a small active sub. @murrayjohnson has something like this and it sounds very nice.
Yeah mine is full of compromise. It’ll never reach the heights of a more complex system with horn bass but it does enough for me. Pays your money etc.
Or ‘life is too short to chase the phantom of perfection only to suffer with disappointment…’
Channelling through you, Japan man is a hypocritical cunt. 
Hahaha
Ten times the price and a tenth the performance 
Both assumptions incorrect but keep telling yourself that 
Thanks for the input all.Will have a rethink.
Will be following this with great interest as my nephew and BiL keep pestering me about compact horns and so far haven’t accepted my response of ‘no such thing’ 
The horns themselves are 60cm across so I want to keep everything within that dimension and inline. I suppose a bit like the Avantgarde
Or sell the horns and amps and other surplus stuff. Use the LV OBXa i have and up grade to a nice pre/power and get my IO1 repaired.
