Yes you can. I have done this with the 2L files on my MC200.

From memory once imported, I added them to an album. I added CD quality files to one album. I added MQA to another (with MQA in the album title). That way when doing some A/B comparisons of CD and undecoded MQA I could see in the Sooloos queue which files were which.

If your issue is that you cannot import from file, then I'm confused other than to suggest the usual power cycle and try again. Presumably the downloaded files play on your computer OK?

I used a Mac to import them, not a PC, but I'd be surprised if that made a difference...

Note I did this before the latest release of Control:Mac/Control:PC ... If I get chance I'll try importing MQA files again.

Various from vintage to SE