Many Pi Hats use their own crystals because the Pi crystal is very prone to jitter.
I have a 5122 Hat and a 3038q2m Hat and both have their own crystals.
Also I just got a TeraDak player which is basically a nice enclosure with a Pi4. It has 2 TCXO’s (which is a lesser form of the OCXO).
As was mentioned, believe ALL modern DACS have their own timing crystals so if you connect via USB you’ll be all set.
I’m not sure if having the Pi have a OCXO or TCXO is any better than some cheaper options (like the one shown on the 5122).
My unscientific opinion is that you need to go way up the audio food chain (streamers >$2k and Chinese DAC > $750 or European / American DAC > $2k) along with a good integrated amp and very nice speakers for it to make a difference).