Blimey!
What brands?!
I tried two consecutive Testor dull coats and I thought it killed the detail on the miniatures... adding another gloss coat in there I can't even imagine!
Just Humbrol 35 clear varnish for the first coat, with a little bit of that army painter stuff mixed in.
For these I used an old tin of Blackfriers matt that I got off a mate, but usually Daler-Rowney.
If you use 3 or 4 highlights the very matt varnish's won't kill off the contrast as much, well, that's what I've found anyway.