[LAU] External Class Compliant Sound Cards

Dear list, I am compiling a list of suitable sound cards for a mobile real-time experimental setup. There are some criteria that such a sound card should fulfil: - External sound card: We have a mini PC with an on-board sound chip. We want to use an external sound card with a decent sound quality. Our mini PC has USB-2, USB-3, USB-C (Thunderbolt 3) connections. - Class compliance: We have a real-time signal processing platform, the Master Hearing Aid, which runs on Linux (Actually it also supports Windows and Mac, but we prefer Linux). Therefore we need a sound card, which Linux can operate. Manufacturers usually do not officially support Linux, but there are some, which run on Linux, because they are class compliant and do not require a dedicated driver. - At least 4 (preferably 6) analog (identical) inputs and at least 2 analog (identical) outputs - Lower sampling rates: As we will do real-time signal processing, we prefer lower sampling rates for the sake of computational complexity. Therefore, ideally we would like to have a sound card, which supports even 16kHz, but 32kHz also OK. I know that these criteria are not easy to fulfil. So far, I couldn't find any sound card, which fulfils all the requirements. In the worst case, we can sacrifice the last requirement and downsample our sound input before processing, but it is a good-to-have one. We would appreciate any suggestion. Thank you in advance. Best Regards, Kamil Adiloglu