When i was looking at things like this (mostly for my pocket computers), they all seemed to have been made "defective by design" by limiting the inputs from the audio jacks. This made them useless for use on my vintage machines.
Has that changed?
As I don't really understand what the issue you had was, I can't answer that question. However the above has separate inputs/output jacks in 2.5mm - for mic and earphone - and it works OK with my JR-100U which was rather sensitive to getting the volume correct. It also is a MP3 recorder, so the files can be accessed as MP3 recordings, or played back as MP3 recordings, meaning they can be "side loaded" into the PC or taken from the PC as audio files that an old computer can read.
What we're talking about is just a bridging gap between using a PC to record and play the sound directly, and having something so I don't always have to use my PC.
I haven't checked for stereo function ( though assume it *might* be stereo ) and whether I need to make a custom cable to avoid shorting a channel, but the reason I got the above was that tape recorder/players cost about $70, and need a tape in them and often an extra power supply, while the above costs about $30 second hand, and at least plugs straight into the computer and can hang off the tape cables and I can just use it and access the audio file later when the old computer is turned off... And it seems to work OK?
The volume is reasonable - or at least it worked for me. And there's manual volume adjustment on it also. These only have 2Gb of recording space, so I'm not sure how many MP3 that is, but it's probably enough to hold the entire JR-100U software library. Only downside is that files are numerical only... No file names.
If you have some more information, I might be able to test it and answer it?