However (simple scenario) if I have a vocalist recording over a multitrack and he has to do a drop in then the level of the vox he has just put down is much lower coming off the recorded track to what he hears when he sings. If I bump up the track gain then of course the new take is recorded at an even higher level so thats a no no.
A trick I do for external monitoring is to use a different mic for monitoring purposes.
That way I can run the mic for recording straight into a Neve outboard preamp (not a mixer) into my interface and have the levels perfectly set.
On a separate stand I have another mic that is not recorded but goes into my Mackie 8.bus for monitoring purposes only.
This only works for mic setups where the mics are stationary. If your singer is singing into a handheld (like a SM7B or soemthing) you will need to use internal monitoring or route the preamp through your mixer for external monitoring.
I have started experimenting with headphone busses and that seemed like an excellent idea EXCEPT when you drop in you cant heaewhats on that track ecause you are now recording to that track and can only hear what is actually being recorded - so thats a no no.
This is all related and I am now back to using an external mixer etc which is fine for a few tracks but when I have 3 or 4 in the studio unless I buy an Allen & Heath desk with 6 aux sends and 24 track input I can't get the HP mix I want/need for all the tracks & people.
I am not sure how much I/O you do have on your mixer (or interface), but you can run a bus out of AA into the mixer for the headphone monitoring (mixed with the extra mic I spoke about above).
I even have the AA click track on all the time running out of it's own interface outputs to a channel of my mixer and control it's volume / muting with the mixer.
To get around the problem of not hearing what you previously did, just make a duplicate track and alternate takes. then once you are done combine them. In AA3 it's even easier just set up one track and duplicate it. In AA2 you will have to manually set up the I/O volume, pan, bussing, etc.
Latency is hugely dependent on the hardware too. MOTU PCI cards are a perfect example. Using a PCI 324 vs. a 424 card there is about a 200ms difference and that can lead to echoing. A 424 card has virtually no delay.