Thanks - found a couple of articles on TB and an interesting quote (which I kind of suspected):
[color=#000000][font=verdana, geneva, lucida,]"Your Bass 400+ is at the all-time pinnacle of bass amps, so forget ever trying to replicate its tone."[/font][/color]
Links below to help others:
[url="http://www.talkbass.com/forum/f15/mesa-boogie-bass-400-a-918437/"][color=#000000][font=verdana, geneva, lucida,]http://www.talkbass.com/forum/f15/mesa-boogie-bass-400-a-918437/[/font][/color][/url]
[url="http://www.talkbass.com/forum/f15/compare-mesa-walkabout-mesa-m-pulse-600-mesa-400-fender-pro-300-a-613872/"]http://www.talkbass.com/forum/f15/compare-mesa-walkabout-mesa-m-pulse-600-mesa-400-fender-pro-300-a-613872/[/url]