I compared the two outputs on my own MF and was unable to hear any difference. The line-level out is balanced, as you'll read in 3.2.1 of the manual. There is a noticeable improvement in noise performance when using this output, but only when it's with a TRS connector cable to a balanced input in a mixer. There shouldn't be any difference in frequency response, so I can only conclude there's a fault.
According to the Numark CM200 USB manual I briefly consulted online, it doesn't appear to have any balanced inputs, unless the two 6.35mm jack inputs for mics are balanced and I didn't see any reference to them being so - the diagram showing equipment connected to the mixer shows mics with TR (tip-ring) 6.35mm jacks, which implies an unbalanced mic input only. But that limitation still shouldn't reduce the bass.
I tried using a standard guitar lead from the line-level out and it sounded fine. You might try that, as it's a simpler connection which would reduce the likelihood of odd dodgy connections with all those adapters.
