The Beocenter 4000 was actually a Japanese device - quite novel though! They do fetch about £125 usually on eBay and about £20 at car boot sales. Personally, I wouldn't touch it. Difficult to keep going as parts are a big problem.
The RX2 is worth about £60 - 75. If it has a cartridge, sell it separately and if you are lucky, that could get £50 as well. Prices are very dependent on condition. Top prices will be on eBay and you need to take pictures and describe the products properly. Having some feedback helps!