Separate names with a comma.
I only saw CX400 and the next line up is sport series.
I don't quite understand this, please clarify.
But I found the MX880, if that's what you're looking for.
If by similar sound quality you mean a similar type of sound signature, the closest I can think of is the CX280/281. The CX485 is similar as well while simultaneously being an upgrade in sound quality, but that's a relatively rare model that is hard to find.
Yes, like MX800 the CX version is CX880. In MX line there are series 4, 5,6 but CX only have 4,6 and next jump is 8 series.
MX5xx is quite a sweet spot for price and SQ so I was thinking about it's CX cousin in similar price range. Of course I have many IME, just curious to try that's all.