Hi Kim,
sorry for taking so long to reply to this - my muting technique is not dissimilar to Michael's, if I remember rightly - I tend to trail my thumb across after my picking fingers, with my thumb sort of pulled back across all the lower strings to mute them as I'm playing (bear in mind, this is only for 'normal' fingerstyle playing, and I do use my thumb to pick about 60% of everything I play, and then the relationship between the left and right hand for muting is a little more complex)
The other advantage of this kind of 'floating thumb' approach is that the angle and position of my fingers in relation to the string that I'm playing is always the same, which makes playing easier...
Muting is vital on all basses, but is much more of an issue when you get far too many strings like we have...
enjoy!
Steve
www.steve-lawson.co.uk