Hi scoobie dooo,
Welcome to the Apeks club:-
There are approx 48 different permutations for layout of a TX apeks, all of them can be of use, with the ATX 100 sort out what you want where, and go for it.
YOU work out YOUR best option, do you want your SPG under your left or right arm, feed for inflators BCD and dry suit, safe second, etc.
Do you want the long hose on your main reg so in an OOA situation your buddy pulls a working reg out of your mouth (thats the way I do it), then you put in the safe second/ octopus. Does the octo go on a bungee round your neck so its there for you
What safe second have you got and it it adjusted so as not to freeflow when not in use (Irecommend something like a TX50 2nd so you can screw in the cracking pressure and turn the venturi down to minimum but you can adjust under water if you have to use it
It all boils down to what you've got and what you need and if you are prepared to spend some time thouht and effort in to getting it right.
Cheer from the other side of the pond
Brian C