I want to re-emphasize a point that was made earlier. If you are are recording loud bands like Tool, you don't need a preamp--all you need is a battery box.
This customer wants to record and I quote "I want my equipment geared towards taping Tool (or other "prog", loud, quiet,loud)"
So yeah a preamp would be a good idea. In this case will he need much gain for loud shows no. My mics put out about -35 at 114db at 1k. So there are lots of reasons why you would want or need a preamp especially if you dont want to use your recorders gain. And like you mentioned there are situations where a battery box will work the only issue is sometimes you never know what you need until your at the venue. So if you have the $$ its better to get something that will do everything. Then something that will only do very loud shows.
I have run CA14 cards AND omnis, and a 9100 preamp, and for the $$$, its BY FAR the best bang for your buck IMO! Like Chris said, you may not NEED a preamp at most times, but why risk it? AND the preamps Chris makes can be used just like a battery box. Just keep the gain low on it and voila, you have a preamp acting like a battery box
And Chris' gear is so cheap compared to most other external mics/preamps, then its VERY AFFORDABLE to just get a CA 9100/9200, especially since he ALWAYS has a sale going on for each and every month. The OP already has the Sony M10, so ALL he needs is a pair of CA mics, whether they are CA11s or CA14s, a CA preamp, and an 1/8">1/8" cable, and BAM, he has a low cost but good quality super small rig
And I disagree with the omnis in small rooms move. There are usually ALOT of drunks at small venues/bars and are SUPER CHATTY most of the times. Running omnis in that scenario is just going to give you a tape with LOUD chatty cathys but amplified 10x
I have run a few diff omni rigs over the years, and Ive NEVER exactly been happy with damn near all of them. 99% of the time I ran omnis, I would have rather run Cards or Hypers
But as always, YMMV and EVERYONE has their own opinion! So I would go to archive.org and listen to as many samples as you can, because NOONE can decide for you, and in the end, YOU have to be happy with YOUR rig, because you'll be the one listening to it the most