Hi Rich,
The improvement was resolution which brought to the surface details that were just not there before. This new information came in different ways, timbre of texture be it instrument or voice was more realistic, the sound space was bigger with more air around images.
Slightly better dynamic shading and also the extension both highs and lows were a little better. These improvements while very apparent IMO in my system was not as profound to me as when I had my DAC6 upgraded to the DAC6/SE. Hope this helps.
Good luck,
Tom