The JVC HA-FW1800 and the Victor HA-FW1500 are the same IEM; those are the international and domestic names respectively. So if you're wondering how the FWX1 compares to the FW1800, just take a look at the graph comparing it to the FW1500.
eyebHere are my measurements of the original FW1800 vs. the FDX1:
(DF-compensated; red = FW1800, black/blue/green = FDX1 filters)
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Since they lowered the FW1800's bass for the FWX1, I'd expect just a moderately warmer low range than on the FDX1 (the original FW1800 is a lot warmer!). Upper mids and lower treble seem pretty similar to the undamped FDX1, whereas high treble looks more restrained than the FDX1.
Overall, you can expect a less analytical, warmer, more mid-focussed and more forgiving sound signature compared to the FDX1. The DLC + wood dome driver, however, is very good, so you'll still get nice detail resolution despite a less analytical tuning.
Boy do I love JVC's Woodie IEM line. I already have HA-FW10000 and HA-FW1800, so I really don't need these - but here I am looking anyways. I'll note that I EQ the Bass down in all of these, so this seems like a natural tuning that matches my preference.