I've never heard the Polks but I like the Helicon 400s. To my ear they are warm and musical, very easy to listen to. Some people feel that the midbass can get a little congested (see Michael Fremer's review of the mk 2s on the Stereophile website) but I have no problem with their bass performance.
They are likely to have a family resemblance to your 800s so if you like the Polks maybe you should keep them so that you have speakers with different sounds so that you can change flavors from time to time.
They are likely to have a family resemblance to your 800s so if you like the Polks maybe you should keep them so that you have speakers with different sounds so that you can change flavors from time to time.