The 901 is a specialized item, nobody else make anything like it, so only armed with generic knowledge I say the EQ that originally came with it, and not any slap-on.
If you can find the Bose EQ that came with the series V speakers then get any EQ that you can get since the Bose has to have EQ of some kind. You won't get Bose to tell you what the EQ curve of the original EQ was so your options are to use spectrum analyzer app or just adjust the sound to your taste.
You will need a way to connect the EQ which is not common on surround sound receivers. You need a tape monitor loop, processor loop, or a separate preamp in - amp out to connect the Eq.