If you happy with the sound of your speakers as they are aside from a desire for greater lower frequency response my suggestion would be for you to add a quality subwoofer to your present system. I have owned Sunfire and REL subwoofers, different models of each, and believe that for sheer bass output the Sunfire line is the better choice, but the REL line will integrate better with your Linn speakers.
A cautionary note:
Once you start with subwoofers, it is hard to go back. They are very addictive
A cautionary note:
Once you start with subwoofers, it is hard to go back. They are very addictive