DIction in choral music

I have an audio-related question.  I'm not sure exactly where to put it here on Audiogon, so I thought I'd put it here under "Music", because while it's kind of a gear-related question, it touches on musical issues.

My wife and I listen to a lot of choral music.  My wife, especially - she sings in choral groups and knows and loves that literature.  We were listening to a piece today and she commented that the words were hard to make out - they were indistinct.

My question is - what factors in our audio gear could be causing that?  I'm going to assume for the moment that the issue is in how the music is being reproduced, rather than in how it was recorded, because my wife has noted this on a number of recordings.

For reference our system is digital files served up from a NAS by MinimServer -> microRendu -> Metrum Musette -> Quicksilver line stage -> Rotel RB-980BX -> Ohm Walsh 1000's.  My first thought is that the Rotel - 25 or more years old at this point - may be past it's prime and may be introducing fuzziness into the sound.  But any and all suggestions are welcome.

Many thanks in advance for your thoughts!