Not sure what you mean by led headroom, who needs headroom in these days of over-compressed tracks with less than 3dB dynamic range. 0dB rulez and Red=Bad. Haven’t used the RB(2) enough to remember if the headphone output is that low. Never read anything about it as a complaint by our readers. Knowing the other Pioneer controllers (I currently own an SX) the headphone amps are usually pretty loud (make sure you set the cue volume in your software high enough though!), to the point that if that isn’t loud enough I start getting worried about hearing damage.
Theoretically I suppose you could set RB DJ to external mixer, set the two relevant output channels to your sound card and operate the controls on the SB and the actual mixing on your Numark M4.
Seems a lot of work though for some headroom and (very) loud headphone levels, bringing two extra pieces of gear (mixer and sound card) with the accompanying cabling.
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