Actually there are at least two different scholars of the LAME developers and enthusiasts.
One scholar believes in the rather old and very rigorously ABX tested LAME version 3.90.3 (not 3.93). You can found many of them at hydrogenaudio forums:
www.hydrogenaudio.org. Especially you should read the MP3 part of their FAQ page
www.hydrogenaudio.org/index.php?showtopic=7516&.
Others are developing the LAME series 3.91, 3.92, 3.93, 3.94, 3.95 and the 3.96, which is the latest "stable" at the moment.
I don't think there is much difference in the audio quality, which is not improved after 3.90.3. The biggest difference is that 3.96 is much faster when encoding VBR files. Some people say that this has sacrificed audio quality in some difficult cases.
I have always used an external MP3 encoder with MC. Currently I use the both LAME versions. My old standard is the 3.90.3. I use it when I like to be sure that the audio quality is the best possible.
When I am in a hurry and I have many CDs to rip and if those CDs are not the best audiophile ones I use v. 3.96, because it is twice as fast.
Today I ripped Queen's Made In Heaven CD. I used the 3.96 because I want to get through my CD collection someday.
After ripping I noticed that high trebles were somewhat distorted. (I think that was intermodulation distortion what I heard). The rip was made with the "--preset extreme --noreplaygain" custom VBR setting. I thought that it was encoder's fault and re-ripped with the 3.90.3 and with the setting "--alt-preset insane" (best 320 kbits CBR). The distortion was still there. So I did third rip to the APE files and noticed that the distortion is actually in the original CD.
So, which version stays on my HD? I have not decided yet. I tried to compare those three versions and it was very difficult to hear any differences. So I probably keep the smallest 3.96 VBR, because I can always re-rip if needed. The album is not one of my favorites anyway.
I my opinion JRiver could safely update the internal encoder to the version 3.96. It is probably the fastest one yet and there are many small improvements and fixes. V. 3.94 and 3.95 were not so good.