I'm very sorry that you found my reply "unacceptably rude". I did not intend offense, I was trying to explain where MrC was coming from (and he also surely did not intend offense).
I'd also like to point out that you've been immediately offended by two of the most helpful (and generally least aggressive) users here on Interact (not to toot my own horn, but I think most people would agree with that statement). So I suspect that perhaps you might need to adjust your "filters" and try to give people here the benefit of the doubt. Most times, here at least, people are sincere and not trying to be rude or aggressive. To be clear, neither MrC or I work for JRiver. We are users like you who are donating our time freely.
I admit, I
was exasperated by your response to MrC's well-reasoned original response, and that certainly came through in my reply. Again, I apologize and meant no personal offense.
As far as your original questions, I believe they've been asked and answered to the best of our ability. Whether something "sounds good" is an entirely subjective query and it is not possible to provide a definitive answer to your query. Both MC18 and MC19 have bit-perfect output, and utilize the same underlying technology with incremental improvements. There are some new features in MC19, which are addressed to some degree in the link MrC provided and other information easily found on this forum.
Especially since MC19 will run on OSX 10.6.8, and since you said you already own a license, I'd stand by the suggestion that you try it and evaluate it yourself. If you want to avoid messing with your existing OSX installation (which is understandable) then
Carbon Copy Cloner and
an external USB hard drive make it extremely easy to copy your existing installation over to another disk, which you can boot and upgrade to 10.9 without impacting your original installation.
Please don't hesitate to ask if you have additional questions that we can answer, but also please bear in mind that it is very difficult to read "tone" in forum posts properly, and try to give responders the benefit of the doubt (at least until they very clearly cross the line, upon which time action will be taken). Thanks.