Depends on what kind of preamp you buy.
If it’s a preamp with USB (or firewire) connection then the soundcard is bypassed.
If you buy a preamp that has only analog output, then you’ll need to connect it to the line-in of the computer’s soundcard.
If you haven’t bought the preamp yet, I’d recommend buying one with usb interface, such as the ART USB Dual Pre. You’ll find quite a lot of reviews of many devices on this topic: https://forum.audacityteam.org/t/sound-card-reviews/8375/1
If you already have a preamp, that doesn’t have a digital connection, then you could consider buying a device such as the UCA-202. Again have a look at the above mentioned topic for reviews.