Wow, thanks Brad! It sounds complicated. So if you were using faders to send to the monitors and then faders for the mix etc, how would make them both sound the same? and isn't that what you would wants vs 2 different sounds of the song, or am i missing what you meant?
The monitor faders are post-tape ("tape" could mean DAW of course), so it would be possible to make them sound exactly like what was coming off tape, and use the faders to change only their balances.
However, sometimes you want to keep the sounds going to tape unprocessed, and add EQ on the monitor side for the benefit of the rough mix, but without committing that EQ to tape.
On a split console it's easy to apply EQ to JUST the monitor path (the aforementioned "jukebox" doesn't always offer EQ on the monitor path, however).
This could be useful if you wanted to apply EQ to the rough mix, but didn't want to commit your EQ to tape. Many inline consoles allow you to do this, as well-- on an SSL 4000, you can choose whether to apply the EQ to the channel path or to the monitor path. You can even split the EQ section and apply the high/low pass filters to one and the rest of the EQ to the other. You can also apply the dynamics section to the channel path or to the monitor path... that way you can choose whether you want to process the sounds for the benefit of the rough mix but leave them unprocessed to tape, to allow the mix engineer flexibility. OR you can process them to tape and box the mix engineer in. Whatever you want to do.
There are many practical reasons besides the rough mix that one might like the process or balance the monitor side differently from what's going to tape. For example-- let's say there's a guide vocal, but the producer in the control room doesn't want to hear it, because she knows the song, and the guide that's going down isn't very good, and she just wants to focus on the track. They can mute the guide vocal (or turn it way down) in the control room without impacting its level to tape.
Or let's say that as the band is running down the first take, the engineer engages a high-pass on the wurli, sweeps it around, then settles on a corner frequency. The first 'rehearsal' take ends up being a magical 'keeper.' Since the engineer tweaked around with the filter only on the monitor side, his twiddling didn't mess up what went to tape, and he can recall his filter setting in the mix if needed. Or let's say there's a particular compressor in the mix room that works well on bass, but that piece of gear is not available in the tracking room. The engineer can use a channel compressor on the SSL "in the meantime" to get a similar effect, but leave the basic sound uncompressed so that he can really dial in the time constants on his favorite compressor later, in the mix suite. Etc etc.