Conditional comments with multiple stylesheets would likely be a better way of handling this, however, I would suggest removing the need to handle this by dropping support for IE6. And while you're at it, drop IE7.
Both IE6 and IE7 have dropped to a point where it generally isn't worth supporting them anymore. If a particular system only runs properly on IE7, IE8+ can still support said systems using compatibility mode.
If dropping support and/or conditional comments aren't applicable, another option would be to include the jQuery Migrate plugin which re-introduces .browser
.