Many customers have noticed that the Windows' PC/SC subsystem is not able to handle more than 10 readers (or slots in case of multi-slot readers). Actually, the SCardListReaders function -the system call to get the list of available PC/SC readers- is limited to 10 readers max. On old versions of Windows it was possible (although complex) to overcome this limitation by grouping the readers in "reader groups" and querying one group after the other. This is not possible anymore, starting with Windows 8.
Microsoft clearly states in KB #3144446:
Starting in Windows 8, the Windows platform supports a maximum of 10 smartcard readers. If more than 10 smartcard readers are available, APIs such as SCardListReaders return a maximum of 10. All other readers are ignored.
So, sorry, but there's no way to use more than 10 PC/SC readers (or slots) on a Windows 8 or Windows 10 system. To make things clear, if you connect 2 SpringCard CSB HSP or 2 SpringCard CrazyWriter HSP with the +3 SIM/SAM expansion board, you already have reached the limit.