I am familiar with the HPM-100s. I may or may have not heard the 60s in my lifetime. You are absolutely right in what you say about two receivers rated the same power, in this case 40 watts, but is the sound quality pleasing. The pre-outs or amp-in may possibly be utilized by you someday. The power amp of the 7140 could power a vintage passive subwoofer in conjunction with one of todays surround sound receivers having a sub output.
I did that with the 3240 int. amp. It is possible that the Kenwood might sound better on the 60s, then the Nad too. I was glad to have helped. Kelsci...