I have owned cls IIZ for 7 years now.When I purchased them,the recommended choices for a sub were the Kinergetics 800,2 tower subs with 8 woofers,excellent but needing extra room and additonal amp or the Muse 18 a single high quality 25x25x25 cube with 2 woofer and included 200 watt amp.I opted for the second one.As additonal bonus they come with a personalized card for the speakers they are mated with.After a lot of experimenting with positioning of the sub( a must!) I reached a good compromise and I can say that the mating of the 2 has been a success especially considering the good but not exceptional size of my room.It cost at the time approx $ 3500,I don't know if they are still in production but are well worthed and you should be able to find them on the used market for approx $ 1500/2000.Check with Muse if the personalized card is still available for your particular series.(II different from IIa and IIz)