At that budget I would go with the Insight all day long. If you keep an eye out for a used one or open box you can save yourself a few hundred on it. Going up, you'll need to hit about the $2k+ range for something that I would recommend.
That being said, keep an eye out for used gear, some really nice "end of production" items do come along at a great savings. I had a Jolida JD9 that was fantastic with the PLX, now
@MikeH has it and I'm pretty sure he's just as happy with it. If you have time, that's a bonus, you can really do a little research based on price, comments and experience here on the forum and so on. I know
@Joe Mac runs Musical Fidelity, and I have great respect for their products as well, not familiar with the M6, but again, you might get some good "used" recommendations to keep an eye out for............the Insight will always be available at $1400, so that's a lock.
I love this set up
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