I've been taping with CA11 Cardioids>STC9000>H320 for a few years now. In ideal conditions my recordings can be great, but in more challenging situations I'm not always happy. I'd lack to do better. The main thing I feel I'm lacking is lots of punch from the bass and drums.
Let's back up a little. The problem is no punch from bass and drums. To me that would point first of all to the mics, or to something rolling off the bass along the way. Make sure any preamp or battery box doesn't have bass roll-off activated. The recorder should be getting what you put into it.
The CA-11 specs do list their frequency response as 20-20,000 Hz, but I would test them and see if the low frequencies are rolled off, because it is difficult to get deep bass out of lower-priced cardioid mics. Do you have (or can you borrow) a musical instrument with bass notes? Or do you have a recording with a deep descending scale (Led Zep, "Dazed and Confused")? Just play a scale going down and see if some of the lower notes start to sound quieter below a certain spot. Concerts are probably going to be using subwoofers that go even lower than 20Hz, but you do want full response at least to 20 Hz.
You probably already know this, but every doubling of the frequency is an octave. So from A440 on a piano, one octave down is 220, then 110, then 55, then 27.5 (the lowest note on a piano). If the mic or preamp starts rolling off the bass at, for instance, 80 hz, you are losing an octave and a half. Check out your original source before you start laying out a lot for a recorder.