XPS 15, UA uad2 pci card

No.  Those are desktop cards - not for notebooks.  Any audio upgrade you want to use will need to be USB or Thunderbolt for your notebook - that is, external.

@1Aka47  The GPU in the XPS 15 is soldered onto the motherboard.  But even in older laptops where that wasn't the case, GPU boards typically connected to motherboards using proprietary designs.  There was an industry standard called MXM that tried to standardize laptop GPU board design, but it never really caught on.

In any case, there's definitely no slot and more importantly no room in a laptop for a traditional PCIe card.  For one thing, where would you expect the connector port bracket on that PCIe card to go when that card was hypothetically installed into your XPS 15?

The only way to use a regular PCIe card with a laptop is to get a Thunderbolt 3 PCIe enclosure.  Companies like StarTech and Sonnet make them, but they are quite expensive.  So if you have a USB option for your audio processor, that would almost certainly be preferable.

However, if you're planning to work with real-time audio, be aware that the XPS 15 models at least thus far have had problems with that.  Google "XPS 15 DPC Latency" and read over some of the articles and forum threads you'll find.  In fairness, DPC latency is not a problem unique to the XPS 15 -- it seems there are quite a few laptops that aren't suitable for real-time audio -- but it seems to be reported more frequently on the XPS 15 than other systems.