Digital BW, The Print

Paul,
I have been trying many different papers with my 1400 and E6 and most 
of the papers have made prints very warm in tone. Today I received a 
box of Premier Art Smooth BW and the prints came out very neutral in 
tone compared to the many other papers I have tried. This paper does 
not look that much whiter than Moab Entrada or other papers but the 
prints are so much more neutral in tone it is amazing. What is causing 
this significant print tone change? Is this an issue related to optical 
brightners? I like the tone very much but just wonder why it is so 
different. Do you have any ideas on this topic? 
Thanks,
Gary W.