I can’t remember specifically what improved but it sounded much better when I implemented AC- link - suggest you try it but make sure you take care and speak with your dealer first as there is a strict process that must be followed for safety
No,,inputs are irrelevant to the AC link, you need to only solely connect the AC link to the output of pre, and only that(in case your pre has dual outputs). It is forbidden to use other amps in parallel to the amp which is fed by AC link(ex. headphone amps etc).
Along some other points of caution.