From my experience with a similarly sized Dell E7440 (13.2" x 9.1" x 0.8") in the Thule sleeve (~14" x 10" x 2" if in the sleeve), it just fits in the Pilot main compartment width wise (14" wide is a comfortable max width for a laptop to fit in a Pilot IMHO).
It does take up most of the space in the main compartment but there is room for file folders and your iPad. Depending on the dimensions of your headphones, it may or may not easily fit in the pilot side pockets or main compartment. Are you transporting your headphones in the protective case? If you can post the dimensions when folded for transport, it will help determine fit better in the Pilot and if it will be bulky.
I posted a few pictures in the post below showing my Pilot loaded up (no headphones like yours) if it helps:
Makers Pilot Comparison
In fact, I would suggest that the Maker's Bag may be better suited to handle your headphones if the width is more than 2.5".
The Pilot will fit in the A45 with all that. The post you read about the simulation of a Pilot fit (that was me) also has TB Customer Service (Beau) confirming the Pilot fit in an A45. It does take up the whole length and height of the main compartment BUT only about half the 9" depth of the A45. IMHO, you should be fine with having 2 pullovers and a jacket underneath as long as they can be compressed to around 4.6 inches thick. The side compartments will also not be impacted but the items in those side compartments will have no wiggle room to expand into the main compartment.
Impressive that you can get all your clothes in the side compartment.
Hope this helps
Cheers!