Looks great Simon!

Is that the medium European solid oak?
Good question, honestly I'm not sure, I just specified solid oak .
I am just working on a quote / design with Simon although 100% solid oak is looking to me a little rich for me at the moment. I've also been considering doors with some smoked glass on the outer two towers although I'm thinking again as the bezel around the edge of yours is very nice!
I don't know who Simon is, at Stump Furniture, you might mean Stuart perhaps?
I went back and forth twice on doors, both glass and solid wood options but because my centre speaker is going in the top centre slot, I couldn't have doors all the way across and every unit I saw with doors on the left and right but open in the middle, didn't appeal to me personally.
I'm really a fan of the very thick "bezel" for sure and nothing obscuring it.
How does the hidden cavity work and how much distance have you left at the back of the shelves for cable drops?
Distance from back of shelves to back panel is 6cm IIRC, but this is entirely your call, I wanted (a) air flow space and (B) plenty of room to drop the cables down the back of each shelf.
The hidden cavity is in the very bottom of the unit, as you look at it face on , part of the bottom shelf "unhooks" and while it looks like only say 3-4 cm under the unit, it's in fact nearly 9cm total space.
The cables from the back of all the equipement drop down , and then all the power blocks, wireless router, gigabit switch, and all that crap are hidden underneath the unit in the cavity.
Its's also quite nice if you want a non visible place to hide your keyboards and what have you.
I was planning on not having a back on mine for the sake of ventilation and ease on installation of kit. Is that something you have factored into your design?
I have a large back panel which is removable (which is the key IMO) . I wasn't concerned about ventilation as the entire front of the unit is open and I left plenty of space at the back behind even the deepest unit (the amp) for breathing space before the back panel, so no issues.
A lot of questions I know. it's the first time I've considered anything like this. I want to get it right and the knowledge of someone else that's already thought about it is invaulable/
Not a problem.
One last thing, I had my shelves adjustable, even 3mm there's a notch.
I also ordered 2 spare shelves so I had flexiblity if needed.
That's about it advice wise that I can give you.
My varnish samples arrive in a couple of days, so I'll have delivery some time next week.
I'll take some nice shots showing it with all the gear on .