Lots of time and paitence.
Are you positive that Beethoven is cat friendly?
Kia has never growled at a cat and for the most part ignores them. I just happened to luck out that I took in a stray that doesn't mind dogs.
When I first took Kia to my parents house, all 5 cats flipped out. They did a lot of hiding. Now, it's not uncommon to find them all sleeping in the same room (as long as Kia doesn't get up abrubtly or bark) That only took about a year to accomplish. 
I took Kia with me this past weekend to stay at a friends house that had two cats. The elder cat ignored Kia while the baby freaked out. He hid the first day and by the 2nd day was still arching his back at Kia but wasn't running away. By the third day Kia had a "shadow". The look on the kitten's face was priceless. He couldn't figure out why this huge scary dog was ignoring him.
As long as you are positive your dog will never attack the cat, then it'll just take time for them to get adjusted.
~Kimmy, Zam, Logan, Raptor, Nimrod, Mei, Jasper, Esme, & Lucy Inara
RIP Kia, Chipper, Morla, & June
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