I'm not sure what you're asking for here. This sentence fragment is a bit confusing:
offer a sliding scale "by increments" that will allow to fine tune say 60 or 63/4/5 etc...?
I'll assume you meant a slider that allows you to select more granular values than the dropdown buffering setting in there now (so "you could set 63, or 4, or 5, or whatever"), and not that 63/4/5 is some kind of crazy vector that doesn't apply here.
Hmmm...
On one hand, the control would work just fine as a slider bar. And the math they use to calculate the buffer size could probably accept any integer value for ms. On the other hand, it would make it just a bit more confusing for "normal people" to fix a problem. Too many fiddly knobs are scary. Too many choices (when you don't know what to pick), overwhelm. If you just have a problem where your music is skipping, MC has a few choices you can pick from (and try one after the other until you find one that is reliable). It doesn't overwhelm with choice, but you can "dial in" the latency a bit.
And there's the rub. The buffering setting only impacts
latency. Unless your DAC's (or its driver) is broken,
the only difference between 100ms of buffering and 400ms of buffering is that when you click Play (or Stop, or change the volume) the higher buffering setting will take 300 ms extra before the music "reacts" and the change is applied.
With a low buffering setting, MC is more responsive. When you hit play, the music starts
faster. When you hit stop, it stops
faster. The downside is that if the CPU and DAC clocks don't match right (or the DAC driver adds additional latency) you can end up overrunning the buffer, which causes a "skip" in the music. Whether you overrun the buffer at a particular setting isn't a function of how powerful your CPU is, generally (unless you have complex convolution DSP effects applied or something), but a function of the DAC and its driver. And, there is already a "lowest supported hardware" option you can pick, if your stuff is fast enough and well behaved enough to let you.
And a human can't easily detect that kind of latency difference when it happens a single time and there is no frame of reference. The scale is too small. There's all kinds of latency within
you, in the same ranges, and it varies depending on what you're doing at the moment. Your visual system has about 100ms of latency, and your auditory system has a different latency (around 30ms). And when you're receiving multiple sensory inputs simultaneously (looking at a button on-screen, clicking on a mouse, and hearing the result) you have even higher latency (depending on the task at hand), often between 130 - 180ms. This has been studied thoroughly, but
here's an interesting paper on the subject [PDF].
So... If you are saying it sounds "better" (what does that mean?) with specific amounts of latency then I'd say either:
1. You are super-human and very concerned about MC feeling responsive when you start and stop playback.
2. Your DAC is broken or has a very cruddy and temperamental driver (which I wouldn't trust anyway).
3. It is placebo.
So...
I don't work for JRiver, and I can't control what they do or do not add to MC, but... The premise of the request seems needless and based on a fundamental misunderstanding of what the buffer does. So color me skeptical.