Yep like frankz said you're talking about bit depth, not bit rate.
Lossless files like FLAC have a fixed bit depth that depends on how they were mastered, normally 16, sometimes 24 or other. Lossy files like MP3 have a "floating" bit depth so the specification really doesn't exist there.
Wasapi Exclusive will pass the file to your audio device with whatever bit depth, sample rate, and bit rate the actual file possesses. It won't get messed with by the Windows Mixer. Wasapi Shared ends up at the Windows Mixer.
And also as already said, your file will only sound as "good" as its original specs are. Altering the stream's bit depth or bit rate or anything else will never make it sound any "better" and usually degrades it.