The sound with the Denon should be slightly brighter and more forward than optimum. The degree to which this appears depends on the rest of your system, your set up, and your expectations.
I had a control on my pre-amp which allowed me to change the load on the fly - the results were quite interesting as you heard the sound go from bright/forward at 47K to dark, dull and recessed at 10ohms. The changes were not ambiguous at all but it was clear to me that I actually liked the load to be a little lower than the range recommended by the manufacturer, probably because my speakers were on the bright/forward side.
In your case the cartridge might sound a bit brighter than optimum. If this is so, you might be able to get someone to alter the Denon by putting some resistors in the phono imput which will reduce its imput to 20ohms. I don't know about your Denon - a lot of phono stages have provision for adding/changing resistors conviently to effect a proper match. FWIW.
