Source and binaries (amd64 and x86) attached.

Pseudocode:

GUID dmo_categories[] = { ... }
for (each guid in dmo_categories) {
    IEnumDMO = DMOEnum(guid, DMO_ENUMF_INCLUDE_KEYED, ...);
    while (0 != items fetched by IEnumDMO::Next(&iid, &szName...)) {
       print iid, szName
    }
}

Output on my system:

>dmoenum.exe
-- Audio decoders ({57F2DB8B-E6BB-4513-9D43-DCD2A6593125}) --
WMAudio Decoder DMO ({2EEB4ADF-4578-4D10-BCA7-BB955F56320A})
WMAPro over S/PDIF DMO ({5210F8E4-B0BB-47C3-A8D9-7B2282CC79ED})
WMSpeech Decoder DMO ({874131CB-4ECC-443B-8948-746B89595D20})
MP3 Decoder DMO ({BBEEA841-0A63-4F52-A7AB-A9B3A84ED38A})

-- Audio effects ({F3602B3F-0592-48DF-A4CD-674721E7EBEB}) --
ParamEq ({120CED89-3BF4-4173-A132-3CB406CF3231})
AEC ({745057C7-F353-4F2D-A7EE-58434477730E})
WavesReverb ({87FC0268-9A55-4360-95AA-004A1D9DE26C})
Gargle ({DAFD8210-5711-4B91-9FE3-F75B7AE279BF})
Compressor ({EF011F79-4000-406D-87AF-BFFB3FC39D57})
Distortion ({EF114C90-CD1D-484E-96E5-09CFAF912A21})
Echo ({EF3E932C-D40B-4F51-8CCF-3F98F1B29D5D})
I3DL2Reverb ({EF985E71-D5C7-42D4-BA4D-2D073E2E96F4})
Flanger ({EFCA3D92-DFD8-4672-A603-7420894BAD98})
Chorus ({EFE6629C-81F7-4281-BD91-C9D604A95AF6})
Resampler DMO ({F447B69E-1884-4A7E-8055-346F74D6EDB3})

-- Audio encoders ({33D9A761-90C8-11D0-BD43-00A0C911CE86}) --
WM Speech Encoder DMO ({1F1F4E1A-2252-4063-84BB-EEE75F8856D5})
WMAudio Encoder DMO ({70F598E9-F4AB-495A-99E2-A7C4D3D89ABF})

-- Video decoders ({4A69B442-28BE-4991-969C-B500ADF5D8A8}) --
Mpeg4s Decoder DMO ({2A11BAE2-FE6E-4249-864B-9E9ED6E8DBC2})
WMV Screen decoder DMO ({7BAFB3B1-D8F4-4279-9253-27DA423108DE})
WMVideo Decoder DMO ({82D353DF-90BD-4382-8BC2-3F6192B76E34})
Mpeg43 Decoder DMO ({CBA9E78B-49A3-49EA-93D4-6BCBA8C4DE07})
MS ATC Screen Decoder 1 ({F1931D8E-51D3-496F-BE8A-3D08AEE9C9DB})
Mpeg4 Decoder DMO ({F371728A-6052-4D47-827C-D039335DFE0A})

-- Video effects ({D990EE14-776C-4723-BE46-3DA2F56F10B9}) --
Frame Rate Converter ({01F36CE2-0907-4D8B-979D-F151BE91C883})
Resizer DMO ({1EA1EA14-48F4-4054-AD1A-E8AEE10AC805})
TOC Generator ({4DDA1941-77A0-4FB1-A518-E2185041D70C})
Thumbnail Generator ({559C6BAD-1EA8-4963-A087-8A6810F9218B})
Color Control ({798059F0-89CA-4160-B325-AEB48EFE4F9A})
Color Converter DMO ({98230571-0087-4204-B020-3282538E57D3})

-- Video encoders ({33D9A760-90C8-11D0-BD43-00A0C911CE86}) --
WMVideo8 Encoder DMO ({7E320092-596A-41B2-BBEB-175D10504EB6})
WMVideo9 Encoder DMO ({D23B90D0-144F-46BD-841D-59E4EB19DC59})
MSScreen 9 encoder DMO ({F7FFE0A0-A4F5-44B5-949E-15ED2BC66F9D})

-- Audio capture effects ({F665AABA-3E09-4920-AA5F-219811148F09}) --