Well, if you want the Marcus tone, you way want to research Atelier Z. They have the actual Marcus tone nailed down with the proper wood, pre and pickup spacing. But yeah, the Sadowsky pre will get you a mother of a slap tone. The combo of everything is out there, and it seems to all be made in Japan - even the Sadowksy Metro..lol. The Japanese apparently love the heck out J basses, and IMO have been making the best ones for years now. I personally think the active Bacchus is better than a Sadowsky Metro in terms of tone and neck, and definitley price. Heck, the Passive Craft J's can be found at crazy low prices and you can just run through a Sadowsky pre if you wanted. There are some 5 string actives that I believe are $1,200 or so. Not sure what you would pay for a Sadowsky Metro, but they are usually over $2k and don't have the same build quality.
Anyway, just so you have options - look at these bad boys -
Bacchus Craft Japan Series - STD-JB ASH5 ver.2 - 5 String Active Bass