I recently bought a Fosi Box X5, after yet again needing to fix up a kit tube phono stage, this time for hum.
I noted its easy ability to swap an op amp in it, and wondered if any difference I might hear would be me expecting to hear a difference or not. My new bias is, it's had a couple weeks to settle in, and while it's not as spacious sounding as my tubed options, it's also more even across the board.
I'll just leave it as is. Subjectively, if a swap makes a difference, I think it could make it sound better with my speakers, worse, or no difference I notice.
The point someone raised about it possibly already using fake op amps is interesting, but so far the reviews I've read have all been positive even if it's so.
So I'm going to leave it as is.