@jdtournier,
I previously installed it using the instructions provided. (I would give it another try).
The information about my filesystem:
Volume name : Macintosh HD
Volume type : Logical Volume
BSD device node : disk1
Mount point : /
File system : Mac OS Extended (Journaled, Encrypted)
Connection : PCI
Device tree path : IODeviceTree:/PCI0@0/PEG0@1/SSD0@0/PRT0@0/PMP@0
Writable : Yes
Is case-sensitive : No
File system UUID : 7EBA2BA9-D067-32C0-9D96-FC2C7CA65F1F
CoreStorage UUID : 24FD0101-129A-41B9-89B2-0622849CC129
Parent CoreStorage LVG UUID : CA9E5E86-7041-4D9B-89F7-34799EACA68E
Volume capacity : 958,809,112,576
Available space (Purgeable + Free) : 723,763,732,612
Purgeable space : 10,105,802,884
Free space : 713,657,929,728
Used space : 235,045,379,964
File count : 2,365,180
Owners enabled : Yes
Is encrypted : Yes
System Integrity Protection supported : Yes
Can be verified : Yes
Can be repaired : No
Bootable : Yes
Journaled : Yes
Disk number : 1
Media name : Macintosh HD
Media type : Generic
Ejectable : Yes
Solid state : No
S.M.A.R.T. status : Not Supported
Parent disks : disk0s2
About anaconda, yes I have it installed 
$which python
/usr/local/anaconda2/bin/python
Now running mrconvert with -nthreads 0 (same as before):
mrconvert before_MR/DWIs_upscaled.nii.gz DWI.mif -grad mr_btable.txt -datatype float32 -stride 0,0,0,1 -nthreads 0
mrconvert: [100%] uncompressing image "before_MR/DWIs_upscaled.nii.gz"
mrconvert: [100%] copying from "before_MR/DWIs_upscaled.nii.gz" to "DWI.mif"
libc++abi.dylib: terminating with uncaught exception of type MR::Exception
Abort trap: 6
About my config file. Are you refering the to mrtrix config file (check below)? If not, I can get it to you as long as you give me some additional clues on where to find it.
cat /usr/local/Cellar/mrtrix3/0.3.15-1397-g93f159a/share/mrtrix3/config
#!/usr/bin/python
#
# autogenerated by MRtrix configure script
#
# configure output:
#
# MRtrix build type requested: release
#
# Detecting OS: darwin
# OS X deployment target: 10.12
# Looking for compiler [clang++]: Apple LLVM version 8.0.0 (clang-800.0.42.1)
# Checking for C++11 compliance: ok
# Checking for ::max_align_t: ok
# Checking for std::max_align_t: ok
# Detecting pointer size: 64 bit
# Detecting byte order: little-endian
# Checking for variable-length array support: yes
# Checking for non-POD variable-length array support: no
# Checking for zlib compression library: 1.2.8
# Checking for Eigen 3 library: 3.2.6
# Checking JSON for Modern C++ requirements: OK
# Checking shared library generation: yes
# Checking for Qt moc: moc (version 5.6.0)
# Checking for Qt qmake: qmake (version 5.6.0)
# Checking for Qt rcc: rcc (version 5.6.0)
# Checking for Qt: 5.6.0
PATH = r'/usr/local/anaconda2/bin:/usr/local/Library/ENV/4.3:/usr/local/opt/pkg-config/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/anaconda2/bin'
obj_suffix = '.o'
exe_suffix = ''
lib_prefix = 'lib'
lib_suffix = '.dylib'
cpp = [ 'clang++', '-c', 'CFLAGS', 'SRC', '-o', 'OBJECT' ]
cpp_flags = [ '-std=c++11', '-DMRTRIX_MACOSX', '-fPIC', '-mmacosx-version-min=10.12', '-DMRTRIX_WORD64', '-DMRTRIX_NO_NON_POD_VLA', '-Wall', '-O3', '-DNDEBUG' ]
ld = [ 'clang++', 'OBJECTS', 'LDFLAGS', '-o', 'EXECUTABLE' ]
ld_flags = [ '-mmacosx-version-min=10.12', '-lz' ]
runpath = '-Wl,-rpath,@loader_path/'
ld_enabled = True
ld_lib = [ 'clang++', 'OBJECTS', 'LDLIB_FLAGS', '-o', 'LIB' ]
ld_lib_flags = [ '-dynamiclib', '-install_name', '@rpath/LIBNAME', '-mmacosx-version-min=10.12', '-mmacosx-version-min=10.12', '-lz' ]
eigen_cflags = [ '-isystem', '/usr/local/Cellar/eigen/3.2.6/include/eigen3', '-DEIGEN_DONT_PARALLELIZE' ]
moc = 'moc'
rcc = 'rcc'
qt_cflags = [ '-pipe', '-stdlib=libc++', '-std=gnu++11', '-isysroot', '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk', '-mmacosx-version-min=10.12', '-fPIC', '-DQT_NO_DEBUG', '-DQT_OPENGL_LIB', '-DQT_SVG_LIB', '-DQT_WIDGETS_LIB', '-DQT_GUI_LIB', '-DQT_CORE_LIB', '-isystem', '/usr/local/anaconda2/include/qt', '-isystem', '/usr/local/anaconda2/include/qt/QtOpenGL', '-isystem', '/usr/local/anaconda2/include/qt/QtSvg', '-isystem', '/usr/local/anaconda2/include/qt/QtWidgets', '-isystem', '/usr/local/anaconda2/include/qt/QtGui', '-isystem', '/usr/local/anaconda2/include/qt/QtCore', '-isystem', '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/System/Library/Frameworks/OpenGL.framework/Headers', '-isystem', '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/System/Library/Frameworks/AGL.framework/Headers', '-isystem', '/usr/local/anaconda2/mkspecs/macx-clang' ]
qt_ldflags = [ '-headerpad_max_install_names', '-stdlib=libc++', '-Wl,-syslibroot,/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk', '-mmacosx-version-min=10.12', '-Wl,-rpath,/usr/local/anaconda2/lib', '-L/usr/local/anaconda2/lib', '-lQt5OpenGL', '-lQt5Svg', '-lQt5Widgets', '-lQt5Gui', '-lQt5Core', '-framework', 'OpenGL', '-framework', 'AGL' ]
nogui = False
((**Also, I have to “\#” all the # chararcters or else they would not appear and will make the text bold. Is there an easier way for future references?))
