Which external USB Soundcard do I need?

Hello OP. How much money can you spend on a new audio interface? You can tell us in your money; we'll convert.

Before buying a used old NI audio interface, make sure they're compatible with your OS. I have an NI Audio 2 DJ I bought in 2013. Does not work with newer versions of macOS. I don't know about Windows. I currently have a Focusrite Clarett 2Pre USB and am generally happy with it, but it's overkill for what you need. The basic Focusrite Scarlett Solo might suit you. I can't advise on how good it is, the Clarett is the only one of theirs I've owned. I had a Roland interface before this that was great, and I only stopped using because it was Firewire and that is no longer a thing, but it was also more than you need. Other brands I see recommended who have relatively cheap simple interfaces: Arturia MiniFuse 1, Universal Audio Volt 1, Presonus Studio 24c. Again, I cannot personally vouch for any of these, only I've heard other people say good things about these brands.

I have an old Focusrite Liquid 56, but now use a UAD Apollo 8P for the desktop and a UAD Apollo Twin for the laptop. The 8P is a nice unit, but it's a rack-mounted unit, so you'll have to accommodate that in your room. I would not recommend the Apollo Twin, because mine gets HOT HOT HOT, even when the computer is just sitting at idle. I think the Twin (at least the one I have) is a fire hazard and should not be left unattended. Mine is usually offline in the art studio for that reason. And it costed $900 new, which is inexcusable, so I'll come out against it EVERY TIME. I should have returned the twin, but I really wanted to be able to use UAD plugins for a laptop or secondary computer.

I also have a couple of old Focusrite and Roland units from the old days. You know, 2-in/2-out+USB MIDI.

All of my audio interfaces can plug into an amplifier with a standard 1/4" cable, but I use powered monitor speakers for better sound and less clutter in an already too-cluttered home.

My first set of powered monitors is a satellite Fostex set with two satellite tweeters and a subwoofer. I think I bought that shortly after the Vikings started exploring North America.

I have some 5" M-Audio BX-5s from the time of the Spanish Inquisition. Those are sitting in my art studio waiting for a computer to be hooked up to. And finally, newest ones are Adam Audio 7" speakers from the about the time that Christopher Columbus discovered the New World. The Adams are nice because they have better natural bass than the BX-5s.

LOL, it feels like this stuff is ancient, and I make jokes about that, but it's not really. It all sounds fine. And I'm a huge proponent of POWERED monitor speakers, because that's one less thing to mess around with.

If you're looking for good used speakers, you might have a look at Reverb or Ebay. I've had great luck buying equipment from both places.

Well, no idea what I could suggest that I have not used or don't know of the actual input/output/feature/budget requirements. This is why I didn't suggest Roland since if you do not need all those inputs/outputs it's likely overkill, just what I use myself. The Roland Quad Capture is the same thing just less I/O and cheaper but I believe it's now discontinued as i've had mine years and that replaced a Presonus Firewire when that became unsupported when Windows 10 released. Main point, start with what your requirements actually are (and future needs maybe) and a reasonable budget and work from there.

I would often go into store and haggle price because it's almost always possible to get a better deal if you ask nicely or shop regularly, an art being lost these days though online shopping and a shame as I have scored some very decent deals in person over the years and learned a lot through just talking to the guys that are usually musicians themselves and other customers around the store. Easy to just spend a few hours chatting with people, most love to chat about what they know.

That seems like a better option than some of the older ones they offered years ago. There were some very cheap models they offered years back and on the Ableton forums people would pop-up occasionally having issues where they could not get both windows/browser audio and DAW audio working and the reason was because those cards needed Asio4All to work with a DAW (they had no drivers of their own) so they were rather terrible. There were some really cheap Akai cards around that were the same too and of course many of the no name brand options are the same. Not knocking Behringer at all, I own DJ amps/speakers, compressors, EQs and headphone amps, all work great and priced well, just always look at the specs and for any audio interface, check the windows driver option. If it lists an ASIO download option, should be good.