Which is better? Recording through a pre-amp or recording up to 192kbps?

Erm, not really sure what you mean here. You can record 192kbps through a preamp…

That said, if you’re wondering about how to record your guitar, directly into your computer via a preamp will be better 9 times out of 10. If you don’t have access to a proper recording interface the Yeti will do you fine, but it might be best to record guitar and then vocals rather than both at the same time, as it’ll make your mix a lot crisper when you do get to mastering.

If you’re simply wondering how to make it louder, though, experiment with upping the gain on your mic and in your DAW, then add compression or volume effects to the track after you’ve recorded. Really, just play around with it a bit.