I can confirm that the mpg321.h (senum) patch is needed on OS X 10.7 (and most likely all other OS X releases). I can't say anything about the IPV6 patch. The listed gist no longer works, so here is the patch:

--- a/mpg321.h  2012-03-25 05:27:49.000000000 -0700
+++ b/mpg321.h  2012-11-15 20:54:28.000000000 -0800
@@ -290,7 +290,7 @@
 /* Shared total decoded frames */
 decoded_frames *Decoded_Frames;

-#if defined(__GNU_LIBRARY__) && !defined(_SEM_SEMUN_UNDEFINED)
+#if defined(__GNU_LIBRARY__) && !defined(_SEM_SEMUN_UNDEFINED) || defined(__APPLE__)
 /* */
 #else
 union semun {
--- a/network.c 2012-03-25 05:27:49.000000000 -0700
+++ b/network.c 2012-11-15 20:58:02.000000000 -0800
@@ -50,6 +50,13 @@

 #define IFVERB if(options.opt & MPG321_VERBOSE_PLAY)

+/* The following defines are needed to emulate the Linux interface on
+ * BSD-based systems like FreeBSD and OS X */
+#if !defined(IPV6_ADD_MEMBERSHIP) && defined(IPV6_JOIN_GROUP)
+#define IPV6_ADD_MEMBERSHIP IPV6_JOIN_GROUP
+#define IPV6_DROP_MEMBERSHIP IPV6_LEAVE_GROUP
+#endif
+
 int proxy_enable = 0;
 char *proxy_server;
 int auth_enable = 0;