Experiencing audio is subjective. If you like it that's all that matters.
If you want my opinion the onboard DAC is holding back untapped fidelity. The onboard amplifier is holding things back. The Bose are holding back quality sound.
A good start into the never ending search for audio perfection is the Audio-Technica ATH-M50x and JDS Labs Element.
Pairing a lower end headphone like the M50X with a very nice amp/DAC like The Element is like using a 1000w Seasonic Prime Platinum for a GTX 1030. :lol:
Best sound quality for $500? Massdrop x Sennheiser HD6XX ( a Sennheiser HD 650 for $200 ) paired with any one of several amp/DAC combos or separates. The Aune X1S drops for $199 on Massdrop once a month or so. Or even better a separate DAC ( Topping D10 or D30, Massdrop x Grace Design SDAC etc - ~$100 range ) and an Aune X7S ( also $199 on Massdrop ). The Element mentioned above would be a great pairing with the 6XX. There are also others in the price range.
Since the amp and DAC are built into the QC35 there's no way to boost sound quality.