Adjustable increments seems like a nice feature, haven't seen it in the Anthems. You may have adjustable input levels which will also affect your output, but it's more important to level match between inputs (if your signal's good you might use the tuner as a reference).
I would be worried if "0" wasn't loud - near as loud as you ever listen (that doesn't mean your system can handle "0", you be the judge of that.) I think you can expect the preamp to be within its capabilities at 0 (unless your input is very high which it doesn't sound like it is.) I regularly listen between -20 & -10, occasionally louder, rarely I've hit 0 and above (and when I do I'm not worried about my preamp).
I would be worried if "0" wasn't loud - near as loud as you ever listen (that doesn't mean your system can handle "0", you be the judge of that.) I think you can expect the preamp to be within its capabilities at 0 (unless your input is very high which it doesn't sound like it is.) I regularly listen between -20 & -10, occasionally louder, rarely I've hit 0 and above (and when I do I'm not worried about my preamp).