Greetings, your best bet would be to ask that question to the people who make your passive pre. Any advise here would be general and may not apply to your application. Not all passive preamps and cables are created egual, so different set-up will vary. As a general rule, "overall" cable length should be cept as short as possible. Also, with a passive pre, it is alway better to bring the amp to the pre and use longer speaker cables, not long interconnect cables.
Happy Listening.
Happy Listening.