adcom gfa-555mkII or W4S ST-500 ? old school vs semi-new school amp. opinions?

I know in the end it will be my ears that determine the choice but I have both on the way.   the adcom is rebuilt and upgraded and the w4s is used. 

I bought the adcom because it was professional rebuilt ground up.  so its reliable and should sound great.

I bought the st-500 because my buddy says D is more clear and has more power. 

ive never had the 555. i had the 545.  ive had crown XLS pro amps but this W4S is probably the most expensive amp. I have had all the usual entry level home amps and several well regarded pro amps. 

I am currently testing a emotiva PT-100 on some Polk RTiA9's .  I am moving from a Crown K1 that is also fresh rebuilt