How to control the font-weight of Source Sans Pro?

hi enfold-team, i want to use the Source Sans pro an have done this:

/*
 * new font in the enfold font-menue: https://kriesi.at/support/topic/new-custom-font/#post-121900
 */
add_filter( 'avf_google_heading_font',  'avia_add_heading_font');
function avia_add_heading_font($fonts)
{
$fonts['Source Sans Pro'] = 'Source Sans Pro:200,300,600,900';
return $fonts;
}

add_filter( 'avf_google_content_font',  'avia_add_content_font');
function avia_add_content_font($fonts)
{
$fonts['Source Sans Pro'] = 'Source Sans Pro:200,300,600,900';
return $fonts;
}

Selected is:
– Heading font: Source Serif Pro
– Defines the Font for your body text”: Source Sans Pro

Now the menue has no bold style anymore and the p-text is very, very thin.
When i try to give them a weight of 600 (via Browser-Style or css), the text is reacting only very minimal.

How can i control the font-weight?