Do SDXC cards need a special card reader, or is software support sufficient?

Given software support, any SDHC card reader is capable of reading SDXC cards.

From Secure Digital # SDXC - Wikipedia:

Compatibility with SDHC

[...] SDHC host devices will accept SDXC cards that follow Version 3.0, since the interface is identical, but the following issues may affect usability:

• SDXC cards are pre-formatted with Microsoft's proprietary and patented exFAT file system, which the host device might not support. [...] FAT32-formatted SDXC cards can be used in a host device built for SDHC if the host device can handle 64GB and larger volumes.

• SDHC host devices will not test the new capability bits defined for SDXC 4.0 cards. It will therefore not be able to use the new features of SDXC, such as transfer speeds above UHS104 (104MB/s).

SD/SDHC/SDXC Specifications and Compatibility confirms this:

SDXC cards will work in SDHC compatible readers (not SD readers) if the computer OS supports exFAT. For more information on exFat see: Operating Systems that support the exFAT File System

The provided link contains information on how to obtain software support for Windows and OS X. For BSD or Linux, exfat - Free exFAT file system implementation - Google Project Hosting may be used.