I think the MX5 is among the very best machines out there; it's light weight, easy to swing, fast recovery and goes deep. Some at Whites have called it a "hot rod in disguise" and I'd have to concur - it sometimes spits and sputters but punches well above its weight. I think the threshold noise is wonderful, but can't help but wondering if it is the noise that kept the MX5 from being a top seller for Whites.
I usually run mine pretty close to the way Hombre runs his: no discrimination, coin & jewelry program, threshold set so it is slightly above a whisper and sensitivity somewhere around 7 or 8. I mostly run mine in 8 tones though and pay close attention to the nickel and above sounds. A quick press & release on the pinpoint button and it is in pinpoint mode (press the button longer and the machine goes into all metal mode). Once the target is pinpointed, a quick press & release of the power button puts the machine in suspend mode. I like that feature a lot, as my Garrett pin-pointer doesn't play well with the MX5. (Whites says the suspend mode locks tracking - so a quick press & release of the power button puts you right back in hunting mode with no worries about the ground balance being off).
It helps if you ground balance the machine - just find clean ground and pump the coil a few times (until the machine settles down) and you'll be good to go. In tough soil that changes often, it helps to stop and ground balance as the soil changes. The machine is always tracking the soil and is good about maintaining a good ground balance, but doing a ground balance yourself will speed that process up a bit (it takes mere seconds).
On faint (questionable) targets I often switch over to all metal just to see if I can get a better idea of what the item could be (tones are disabled in all metal, but VDI remains).
You can set the machine up to cherry pick* (if you wish) - just discriminate everything out to +50, set one tone, and dig almost everything that beeps. You'll lose nickels doing this - so pay attention to threshold dropouts and the VDI (nickels usually come in at 19 - give or take a bit).
You can also set different discrimination patterns* on the C&J/Beach programs, then switch (with a press of a button) between the two programs to get a better idea of what the target is. (Run open in C&J and a high trash discrimination pattern in Beach - that way you won't lose small gold).
* These two methods of hunting are not my idea. The concepts are ideas mentioned by deolslyfox over on Whites Electronics (their forum). I sometimes cherry pick targets, but I do so by listening to the high tones (8 tone setup) and isolating targets from trash by way of swinging slow and carefully. I will use the 4X6 coil in really trashy areas but mostly hunt with the spider coil that comes with the MX5.
The stock setting (volume) is far too loud for me (using headphones). I believe stock is around 20 - I run the volume around 8 or so. I also turn VCO on in pinpoint mode (press pinpoint button and up/down arrows to change between VCO on/off when pinpointing).
Press power button + Beach button to reset current program to factory settings.
Press power button + Select button to reset all to factory settings.
Good luck. I think you'll love your MX5. I know I love mine.