You should be able to get $6,600 off either an Advance or A-Spec Advance without any issues. I have also seen $6,600 off A-Spec.
For instance, I just purchased a 2025 A-Spec Advance in Pearl White with Red interior at $6,746.94 off the MSRP. The dealer honored my color choice, and I ended up paying $63,253.05 for the car, with an out-the-door (OTD) price of $67,000, which includes state and county taxes, doc fees, and registration/tags.
Additionally, I was able to negotiate 15% off all accessory parts and their installation.
My strategy was to start with the Navy Fed TrueCar offer and then use that to get competing dealers to submit better offers. I also found that websites like Gargurus and Caredge provided great information to help guide my negotiations. While I could have probably saved another $200-$500 if I had pushed a bit more, I decided that time is money and I had already spent enough time on the shopping process.