With the E minor shape the 4th string buzzes right?Yeah,been there..For that,as you''ll hear from many fellow IGTians,you'll have to practise a lot...other than that learn songs which involve such chords like Gm (eg Days go by) If you keep playing the chords in a good tempo,you won't even notice when you got the barre right..
Also try playing the G Scale (from 3rd fret of 6th string) by completely barring the third fret throughout the whole scale,that'll increase the barring strength..
As usual go for accuracy and timing rather than speed..make sure no buzzes are heard and use a really really slow tempo...
About the A major shape,strings 2,3 and 4 can be barred by the third finger instead of using a finger for each of the strings...
I recommend though,that you use a finger for each string..you're probably barring all the six strings completely,remember you're to focus the barre only on the 5th and 1st string (sixth doesn't get barred in A shape) and you can apply relatively less strenght on the rest of the strings in between..
The obvious advice is practice,but I hope the rest of what I said will also be useful.
"I feel like I'm number one,yet I'm last in line..."
"So I think I'll keep on walking,with my head held high...
And only God knows why..."
Only God Knows Why - Kid Rock