If you want to have eloquence working with NVDA, you can follow these steps.
Note : The following instructions have been taken from the french NVDA community site
Source
1. Download NVDA-eloq.zip
2. Extract all files to the directory userConfig/synthDrivers of your NVDA installation (it works for portable USB installations too)
3. IN the eloquence subdirectory, paste ECI.DLL, ECI.INI and the *.SYN files corresponding to the languages you want. For english, it's en.syn, enu.syn, en50.syn or enu50.syn (one of these)
You have to take these files from a program that already use eloquence : jaws, openbook, IBM home page reader, etc.
If you installed jaws, you will find these files in C:\Program files\Freedom scientific\Shared\Eloquence\6.1\
4. Restart NVDA. You should now be able to select eloquence in the synthesizer preferences
There are 10 kinds of people : those who know binary, and those who don't.