JHenryF3, first there IS a new W10 card reader drive for the XPS 8700. It is sort of hidden under Removable Storage. The file is Dell Platform Tags Utility (I'm sure by the name you would KNOW what you want it for, just like the old one was FoxConn Icon Manager!).
This is a sort of strange one too, only when you insert a card into a slot will it appear.
When I went to W10 my card reader didn't 'seem' to work either. My PC was under Warranty and I was sent a 'cheap' USB 3.0 3 slot reader that covers Micro SD, SD/SD HC/SDXC/MMC, and MS/MSXC card. Amazon has it for less than $11, http://www.amazon.com/StarTech-com-External-Memory-Reader-FCREADMICRO3/dp/B00DFVZOCA
Did you go to the Intel site and run its checker to verify that you had the Windows 10 drivers installed for the Intel Lynx Point (Z87) chipset? IrvSp is correct, we did release a Windows 10 Foxconn Icon Manager for the Foxconn 19-in-1 Media Card Reader. Did you install it?
Foxconn Icon Manager
Version 10.0.10125.31214, A00
Chris, that is the file I got, but check the NAME for it, it is NOT Foxconn Icon Manager. Only when you open APPLIES TO will you see Foxconn Icon Manager (why isn't it called 19-in-1 card reader driver?).
By the way, under W8.1 with the OLD FoxConn driver the 4 slots ALWAYS showed in My Computer or Explorer. Now with the new driver ONLY when a card is in. Not a real problem but it does work differently.
Chris & IrvSp,
Thank you for your help, but I still can't see the card reader in my Device Manager, and it doesn't show up in Windows Explorer if I insert an SD card in the slot. The only thing I can see under "Disk Drives" is "ST1000DM003-1ER162". i can only see the other card readers if I click "Show Hidden Devices" (except for the "miniMMC/SD/RS/SDXC", which does not appear at all since I uninstalled it; I thought I needed to do that to update the driver).
Anyway, I just ordered this 3.0 media card reader from Amazon ($5.89): http://www.amazon.com/gp/offer-listing/B00OJ5WBUE/ref=dp_olp_new?ie=UTF8&condition=new