I "hear" the Gen 2 Bose upgrade is better than the Gen 1 with Bose. I do not know from personal experience as I have a Gen 1 with Bose and it's "ok"--but the subwoofer really doesn't add much low-end depth.
I test-drove a Gen 2 (no Bose) and the stereo was adequate--I would say just slightly less than my Gen 1 with Bose.
I would bring your music with you on a test drive so you can do a realistic comparison among systems.
I have a Gen1 Volt (2015) and Bolt, both fully loaded included Bose speakers.
The sound system in the Bolt is definitely better sounding.
I drive the Volt most days, and my husband drives the Bolt. I drive the Bolt only on weekends usually when we are together, and the better audio is always fairly noticeable for me even on compressed Sirius XM classical audio channels.
I could not comment about subwoofer, I don't know if it actually ever comes on for what I listen to, not sure how the equalizing is done. But both lows and highs sound better in the Bolt, to me.
I drove the Bolt today for a few hours and heard a slight bit of hiss at medium high volume. I think likely because it was an old recording of Christoph Eschenbach on piano, and he is already fairly old. The date of the recording was not stated. I can't remember which Mozart piece he was playing specifically. Ie. noise was likely at the source, not in the audio system.
Have not done comparisons between lossles audio and lossy from the USB drive. WMA lossless works . I can hear the difference between lossly and lossless on a friend's very expensive audio system - I can pick the uncompressed version every time in blind test ... Tough to do that in a car while driving, though

Maybe in the rear seat with someone in the passenger seat changing between files.