The problem is that Apache doesn't know what to do with those values, hence the internal server error. You need to change the lines to the following:

1) php_value suhosin.post.max_vars 8000

2) php_value suhosin.request.max_vars 8000

The php_value causes the setting to be passed along to PHP. If you were setting boolean values (true/false), you would use php_flag instead. This will only work if you are running PHP as an Apache module. Otherwise you have to edit the php.ini file, which may not be an option.