@vinylrecord61, You received 27 suggestions recommending Class A/B, Class D and class A. In addition, you received specific recommendations for various brands of amplifiers (excellent information). Most every post I saw highly recommended something and was very useful.
Your original question was "what am I going to experience putting a Class D amp with a hundred watts per Channel in place of my Onkyo with 140 watts per Channel at class A B power?an easy process?”. Based on these 27 posts, I do not know if we actually answered your question. I will say you received many useful and different opinions.
Since you are unable to visit your local retailer, I suggest you contact a retailer (local, if possible) that will loan you two amplifiers, class D and Class A/B, for you to demo in your listening room.
Please remember it is your system, your environment, your budget, your other equipment and listening that decides what to purchase. It is not an easy process. Please keep us posted.