I think you are right Geoff, but it is only very occasionally apparent so It isn't a big issue for me. I'll take that bit of edge over an overly smooth presentation any day.
I'm waiting on the IMF being sorted before I make a decision about where to go with the speakers. Options are
1) use the IMFs if they are up to scratch once recapped.
2) Use the Akais with a better sub than the Yamaha I have now - possibly two subs using the same Akai bass drivers with active crossover, or possibly 2 passive - but large (100 litre) subs and tagged on to the existing Akai crossovers.
3) use the B&O, again with a better sub either built or bought.
4) buy some more speakers.