The M series was always ported if I remember correctly, as was the MC400. The original Newton towers, T300 and T500, were sealed with a separate sealed chamber for the woofers/passive radiators, while the later passive towers (T100 and T200) were ported. MC500 was sealed as it was made to match the T500. All the plastic speakers (MC50/100/200/300/S100/200/300) were sealed. The Model 6 is and has always been sealed as it is considered to be a modern Advent-like speaker.
The Newton subs were all sealed, with the P500/1000 having the dual woofers in a push-push/pull-pull configuration. Bob Hazelwood posted on another forum that the two drivers canceled each other out so there would be no enclosure noise/resonance. P200 (which I have and still use in my 2 channel system) was a standard single driver sealed sub, but it too has very low resonance. The Basscube 8 was ported but I'm not sure on the others. I think the 10 and 12 may have been sealed and the 15 had dual porting?
And I agree about the tweeter, and I do like it honestly, but compared to what I have now it just isn't as detailed. I really do like the M80s, I think they're a great speaker that can compete with others way up the ladder, but ultimately the detail I get from the Wharfedales is just something they can't do, at least in this room.