You can find some in single elements if you create an init AWM2 and edit the element you can do a category search for elements. There you can find all of the choir elements. There are a bunch and I think it has you covered if you know how to tweek synth envelopes and such you'll have a lot of options. If not just check under the choir and pads section and go to choir in the category search. If you look at the edits of these parts you will see what elements make up the different voices. Hope that helps. I am sure a more detailed answer will come from Jason or Bad Mister.

I was interested in choirs as well. I don't have the MODX yet but took a look at the waveform list in the MODX Data List PDF. There is complete list of choir/voice waveforms including ahhs, oohs, and all the shoo bee doo type of scat voices. It looks like a pretty complete list to me, unless one is looking for some specific kind of female or male voice sample.

Review the data list to see what sounds are available in single "sample" form. Take a look at the "voices" Performances to see if anything works. There's a Choir/Pad main category with Choir as the sub category.

514 Choir Service Pad/Choir Choir
515 Gospel Hmm Pad/Choir Choir
516 Gospel Wow Pad/Choir Choir
517 Gospel Hey Pad/Choir Choir
518 Latin Vocal Pad/Choir Choir
519 Jazz Singers Pad/Choir Choir
520 BoysChoir MW Xfade Pad/Choir Choir
521 FM Choir Pad/Choir Choir
522 Choir/Str/Pipe Org Pad/Choir Choir
523 FM Linear Synth Pad/Choir Bright

You should be able to start with one of those likely AWM2 Performances (sampled, not FM-X) and build what you're looking for from it.

On the sample ("Waveform" ) side, there's a bunch of sounds to choose from (Pads main category, Voice sub category):

1922 Hah Choir St Pads Voice
1923 Hah Choir L Pads Voice
1924 Hah Choir R Pads Voice
1925 Ooh Choir St Pads Voice
1926 Ooh Choir L Pads Voice
1927 Ooh Choir R Pads Voice
1928 Ooh St Pads Voice
1929 Ooh L Pads Voice
1930 Ooh R Pads Voice
1931 Ooh St Of Pads Voice
1932 Ooh L Of Pads Voice
1933 Ooh R Of Pads Voice
1934 Cho Breath L Pads Voice
1935 Cho Breath R Pads Voice
1936 Syn Vox Pads Voice
1937 Vox Noise Pads Voice
1938 Itopia Pads Voice
1939 Granu Vox Pads Voice
1940 Day Pads Voice
1941 So Long Pads Voice
1942 Vocal Osc Pads Voice
1943 Boys Choir Oh p Pads Voice
1944 Boys Choir Oh mf Pads Voice
1945 Boys Choir Ah p Pads Voice
1946 Boys Choir Ah mf Pads Voice
1947 Gospel Choir Hmm f Pads Voice
1948 Gospel Choir Wow f Pads Voice
1949 Gospel Choir Hey f Pads Voice
1950 M Bah Soft Pads Voice
1951 F Bah Soft Pads Voice
1952 Mix Bah Soft Pads Voice
1953 M Bah Loud Pads Voice
1954 F Bah Loud Pads Voice
1955 Mix Bah Loud Pads Voice
1956 M Hah Soft Pads Voice
1957 F Hah Soft Pads Voice
1958 Mix Hah Soft Pads Voice
1959 M Hah Loud Pads Voice
1960 F Hah Loud Pads Voice
1961 Mix Hah Loud Pads Voice
1962 M Yah Soft Pads Voice
1963 F Yah Soft Pads Voice
1964 Mix Yah Soft Pads Voice
1965 M Huh Soft Pads Voice
1966 F Huh Soft Pads Voice
1967 Mix Huh Soft Pads Voice
1968 M Huh Loud Pads Voice
1969 F Huh Loud Pads Voice
1970 Mix Huh Loud Pads Voice
1971 M Huh Vib Soft Pads Voice
1972 F Huh Vib Soft Pads Voice
1973 Mix Huh Vib Soft Pads Voice
1974 M Huh Vib Loud Pads Voice
1975 F Huh Vib Loud Pads Voice
1976 Mix Huh Vib Loud Pads Voice
1977 M Dooh Soft Pads Voice
1978 F Dooh Soft Pads Voice
1979 Mix Dooh Soft Pads Voice
1980 M Dooh Loud Pads Voice
1981 F Dooh Loud Pads Voice
1982 Mix Dooh Loud Pads Voice
1983 M Shoo Soft Pads Voice
1984 F Shoo Soft Pads Voice
1985 Mix Shoo Soft Pads Voice
1986 M Whee Pads Voice
1987 F Whee Pads Voice
1988 Mix Whee Pads Voice
1989 M Eeh Vib Pads Voice
1990 F Eeh Vib Pads Voice
1991 Mix Eeh Vib Pads Voice
1992 M Bee Pads Voice
1993 F Bee Pads Voice
1994 Mix Bee Pads Voice
1995 M Dah Soft Pads Voice
1996 F Dah Soft Pads Voice
1997 Mix Dah Soft Pads Voice
1998 M Dah Loud Pads Voice
1999 F Dah Loud Pads Voice
2000 Mix Dah Loud Pads Voice

2001 Vocal Breathing Pads Voice
2002 F Bah Soft -12 Pads Voice
2003 F Bah Loud -12 Pads Voice
2004 F Hah Soft -12 Pads Voice
2005 F Hah Loud -12 Pads Voice
2006 F Yah Soft -12 Pads Voice
2007 F Huh Soft -12 Pads Voice
2008 F Huh Loud -12 Pads Voice
2009 F Huh Vib Soft -12 Pads Voice
2010 F Huh Vib Loud -12 Pads Voice
2011 F Dooh Soft -12 Pads Voice
2012 F Dooh Loud -12 Pads Voice
2013 F Shoo Soft -12 Pads Voice
2014 F Whee -12 Pads Voice
2015 F Eeh Vib -12 Pads Voice
2016 F Bee -12 Pads Voice
2017 F Dah Soft -12 Pads Voice
2018 F Dah Loud -12 Pads Voice
2019 Bah Soft Split Pads Voice
2020 Bah Vib Loud Split Pads Voice
2021 Hah Soft Split Pads Voice
2022 Hah Loud Split Pads Voice
2023 Yah Soft Split Pads Voice
2024 Huh Soft Split Pads Voice
2025 Huh Loud Split Pads Voice
2026 Huh Vib Soft Split Pads Voice
2027 Huh Vib Loud Split Pads Voice
2028 Dooh Soft Split Pads Voice
2029 Dooh Loud Split Pads Voice
2030 Shoo Soft Split Pads Voice
2031 Whee Split Pads Voice
2032 Eeh Vib Split Pads Voice
2033 Bee Split Pads Voice
2034 Dah Soft Split Pads Voice
2035 Dah Loud Split Pads Voice
2036 ScatCycle1-1 Pads Voice
2037 ScatCycle1-2 Pads Voice
2038 ScatCycle2-1 Pads Voice
2039 ScatCycle2-2 Pads Voice
2040 ScatCycle3-1 Pads Voice
2041 ScatCycle3-2 Pads Voice
2042 ScatCycle4-1 Pads Voice
2043 ScatCycle4-2 Pads Voice
2044 LatinCycle1 Pads Voice
2045 LatinCycle2 Pads Voice
2046 LatinCycle3 Pads Voice
2047 ScatCycle Split1-1 Pads Voice
2048 ScatCycle Split1-2 Pads Voice
2049 ScatCycle Split2-1 Pads Voice
2050 ScatCycle Split2-2 Pads Voice
2051 ScatCycle Split3-1 Pads Voice
2052 ScatCycle Split3-2 Pads Voice
2053 ScatCycle Split4-1 Pads Voice
2054 ScatCycle Split4-2 Pads Voice
2055 LatinCycle Split1 Pads Voice
2056 LatinCycle Split2 Pads Voice
2057 LatinCycle Split3 Pads Voice