@localfrs – Sorry we missed your post.
You can follow these instructions to change thumbnail size of the avatars –
http://buddydev.com/buddypress/changing-default-avatar-size-croppedused-by-buddypress/
Note that this will only affect newly uploaded images though. Once you do that, I believe you will need to change the CSS by going to Appearance>>CBOX Theme Options>> Custom CSS>>Global>Custom CSS and adding something like this:
.activity-list li.mini .activity-avatar img.avatar, .activity-list li.mini .activity-avatar img.FB_profile_pic {
height: 150px;
margin-bottom: 20px;
width: 150px;
}
(I think the activity stream displays 40 x 40 – the change above would make it 150 x 150)
I you just want to make them a little bigger, try just with the CSS – you will lose some resolution though, I think.