Tiger,
I'm wondering if you could use a preamp-processor with the 502A since it's an integrated amp, and I don't believe you can separate the 502A preamp from the power amp?
Greq,
If you want to keep the Jolida sound for home theater, you could purchase one of Jolida's "Model JD 1704RC which is a "remote control three channel integrated hybrid amplifier with a control channel for the subwoofer". Specs on it can be found on Jolida's site but I believe it offers 75 watts per channel.
Add your Jolida 502A tube integrated amp (btw, I also own one), or a Jolida 1501RC if you want to keep the 502A just for stereo, and a DVD player with a built in processor, along with subwoofer, center and rear channel speakers, and you're in business.
Anyway more info on the 1501RC and 1704RC can be found on the Jolida site. As for particular question about integrating your 502A and 1704C into a Home Theater set-up, I would simply send an e-mail to Michael Allen at Jolida. He's real good about getting back to customers and answering questions.