What's the problem with the midrange? How is it differing from what you want to hear?
Have you tried repositioning your speakers? What's your room like - as in, are there any soft furnishings or is it more of a contemporary, clean-cut design with lots of bare surfaces - wood floors, etc?
Go back to basic with the whole arrangement before lashing the cash on anything else. Also, ask your dealer (if the speaker repositioning doesn't work) what he can suggest. Did you buy everything from the one dealer?
Chord Odyssey speaker cable...okay...here's another "back to basics" suggestion. Get some generic speaker wire. Single strand copper core, or some basic stranded stuff. NOT bell wire, that's not the point of the suggestion. Failing that, Audioquest Type IV (or similar, it's not the brand that's important, it's the cable construction you're interested in here) - I use this and have done since the late 1990s and my stereo's sound quality is excellent (for what I want to hear).
I'd be inclined to unplug the Tacima for now as well. If you do need a block, you can always plug it back in later. Alternatively, try out one of the unbranded white blocks you see in B&Q. Yes, the ones that are less than a fiver. You probably already own one.
The point isn't to debunk "accepted" hifi theory, it's crossing off all the options you can try right now that don't involve extra spend, or very minimal in the case of new speaker wire to help the system deliver what you're looking for. You can always add these bits back in later on.
In case you're wondering, I'm somewhat sceptical of the benefits offered by expensive cable accessories - another issue for another thread however - but trying out cheaper alternatives will give you the chance to compare and contrast without breaking the bank.
Your problem seems to be more one of getting your system to meet your expectation, as somewhere along the line, what you want and what it's delivering went their separate ways.
Ticklist:-
- speaker reposition
- room furnishings
- unplug mains conditioner
- generic speaker cables
- understanding what you want to hear in contrast to the sound being delivered.
Hope that helps (in some/any small way)! And you can of course keep your existing wires in place until you're sure that the 'free' suggestions aren't at fault. So reposition the speakers and chuck the cushions round the room with nary a backward glance. Okay, your other half will give you hell, but hey, sweeten the deal and make the dinner...!