Klh r5100 how do I know what size speakers to use with the klh r5100?

Depending on the watts on your stereo would tell you the most, for example say its 300 watts u buy a 150 watt speaker it would blow the speaker, if you buy a 500 watt speaker your risking frying the stereo, it be best too even it out as best you can, i know that this has nothing to do with what ur asking but it would help you to save more money on buying a new speakers or receiver, now to the answer to you question, i would recommend a 12inch speaker, it would give you good sound quality