Need help with 3-way wiring (diagram included)
What you have here is a line-side traveller loop.  The white wire in the leftmost 14/3 cable takes power out to the switch in Box #2, while the red and black wires in that cable are the travellers going back to the switch in Box #1, which then feeds the load.

The fortunate thing about this configuration is that it's relatively easy to hook your smart switches up to it.  You'll just need a couple of pigtails for the line and neutral on your new dimmer, and a couple of wirenuts to cap off the unused black wire in the cable between the two switch boxes.


Make sure the power's off at the breaker.
Remove the old switches.


In the first box:


Remove the white wire that's bundled in with the black wires from that junction and join it and the white pigtail to the existing bundle of white wires.  (These are your neutrals.)  Remove any tape or paint flags or markings on the white wire in the leftmost cable.  It will become a neutral once again, as it was a hot previously.
Nut the black pigtail into the existing bundle of black wires.  (This is your hot feed coming into the box.)
Connect the existing ground pigtail that grounded the old switch to the ground terminal on the smart switch if the old switch was grounded.  If it was not grounded, post a comment here and I'll update the instructions.
Connect the black pigtail to the line terminal on the smart switch.
Connect the white pigtail to the neutral terminal on the smart switch.
Connect the red wire from the leftmost cable to the traveller terminal on the smart switch.
Cap off the black wire from the leftmost cable with a wirenut.
Connect the red wire from the center cable to the load terminal on the smart switch.


In the second box:


Remove any tape flags or paint markings present from the white wire.
Cap off the black wire with a wirenut.
Connect the ground wire (if present) to the remote's ground terminal.  If no ground wire is present, post a comment here.
Connect the red wire to the remote's traveller terminal.
Connect the white wire to the remote's neutral terminal.
Put everything back together in both boxes.
Turn the power back on and configure the smart dimmer.