Ebay and Amazon can also work well for less exotic items from brands with high name recognition. From your list, I'd say the Rega turntable would do best there down to the Sony equipment as the least likely to move, because Sony covers a broader field and is not known exclusively for high end equipment.
My experience has been that on Amazon, selling items that are still in current production can yield the highest transaction prices because folks are comparing your item to the cost of a new one. In the past few years I'd done much better via Amazon than Ebay, but recently that was reversed and I sold everything on Ebay ... guess it depends which way the wind is blowing.
It bears mentioning that there are nasty, dirty, low down, unscrupulous people out there though. Document the condition and serial number (etc.) of your item scrupulously to avoid being ripped off and good luck.