How to Make my Cydia Tweak Work on iPhone 6?

I have a tweak on cydia called Don't Kill the Beat. It forces apps to allow music.app to play audio instead of automatically pausing. It works on iPhone 5S and below, but not the iPhone 6. I find it hard to believe because the 5S and 6/6+ have the same architecture (arm64). Here is my code:

    #import <SBApplication.h>

%hook SBApplication

- (bool)supportsAudioBackgroundMode { return TRUE; }

%end

And here is my makefile:

export ARCHS = armv7 armv7s arm64
export TARGET = iphone:clang
export SDKVERSION = 7.0
export SDKVERSION = 8.1
include theos/makefiles/common.mk
TWEAK_NAME = DontKillTheBeat
DontKillTheBeat_FILES = Tweak.xm
subprojects=dontkillthebeat

include $(THEOS_MAKE_PATH)/tweak.mk

after-install::
    install.exec "killall -9 SpringBoard"
include $(THEOS_MAKE_PATH)/aggregate.mk

How can I get it to work on iPhone 6/6+? I appreciate all ideas.