Hi,
I can help with regards to the Meridian equipment. Pricing depends on condition as well as version of electronics inside the speaker. Please look on the backs of the speakers- both of those models were originally released as 18-bit ones, but could be upgraded to the 24 bit versions. If you see a sticker on the back that says 96/24 then they are a later version (either from the factory or upgraded) and are worth more. The sticker denotes that the electronics within the speaker have been upgraded to support 24-bit 96kHz sampling.
You can also look to the displays, older speakers have a 7-segment display, while newer versions have a dot matrix display. All dot matrix displays are the 96/24 versions.
Assuming they are in good shape, no major flaws, have grilles and glass with no cracks, the DSP6000s (96/24 version) are in the $2,000-2,700 range. The 18-bit ones (without the sticker) are in the $1,200-1,900 range.
For the DSP5000C, this one unfortunately isn't worth much. A perfect one 96/24 from the factory goes for the $350-$500 range. The 18-bit version (again without the sticker) goes for $200-325.
While these are older speakers, they sound incredible when correctly set up! The original retail price of the 96/24 versions of the DSP6000s was $24,995.00 and the retail on the 5000C was $4,995.00. These were very expensive when new, but also note this was over 20 years ago and current resell values account for depreciation.
If the owner had the original boxes it will also help the sale. The DSP6000s are about 140 pounds each, so without the boxes, you are stuck to a local sale or will have to have them crated to ship safely at added expense.
How are you planning to sell these?