[Doug Young]

I have no experience with an H2 or the lower end Zoom products, I've used the H4n and have an H6 now (thinking of upgraded to the H8 or F series soon). The H6 was a noticeable step up in noise and sound quality from the H4n. If you're talking about the H5/H6 or newer, I don't think you'd find that the preamps limit your mics. There's certainly the whole "weakest link" issue, but it's not like the Zoom preamps are so bad that they'd limit what you'd get out of better mics, the mics will still matter. Actually one of the biggest benefits of external mics is the increase in placement options. Mic choices gets somewhat subjective, but it's easy to hear the difference between being stuck with XY and being able to do spaced pairs, or other micing techniques.

I posted a comparison between preamps a while back here - can't locate it right now. What I recall was that all of them sounded "fine", and it you just listened to the Zoom, it sounded good. If you compared the Zoom preamps to my "better" preamps (same mics), there was a small but noticeable difference. The Zoom seemed a little "flatter" and less dimensional or something. I could hear it, and people listening here had no problem picking out the Zoom blind, as the "lesser" preamp. But that's comparing preamps, not exactly what you're asking.

I record all my You Tube videos with a Zoom H6 and various external mics, so check out my you tube channel if you want (link below, I think) and you can hear at least one person's example of H6+external mics. I wouldn't hold them up as perfect recordings, but you can see if you think they are adequate or not as one example. If I recorded these with better gear, presumably they'd sound better if you A/B'd them, but since you can only hear the Zoom, you'd just have to decide if they sound good enough, or if you think they are obviously limited by the Zoom.