I have been gigging 2 acoustic guitars with LB6 and a Baggs pre-amps on stage for well over a decade and am very happy with the sound. Infact they've attracted numerous positive comments about the quality of the amplified sound. Generally I've DI'd the guitars straight thru the desk with a flat channel EQ and a little effect. I use the sweepable mid-range regularly to fine-tune to different rooms and PA EQ patterns.

My only problem has been that at the foldback volumes needed in noisier rooms (eg. busy pubs), both guitars feedback in the lower G to B range (98 - 120Hz). My luthier tells me that this is a common resonant frequency in acoustic guitars. You know the scene - you forget to drop the volume on the instrument and saunter off stage to grab a beer and the A string takes on a life of its own until its banging like a barn door in a gale.

I've regularly used a soundhole plug, and this makes a small difference, but not enough. Cutting the bass level on the preamp solves the problem, but it robs the guitar of the warmth that I'm after by using an acoustic guitar in the first place. I've found that cutting that frequency range at the 31band EQ post-desk works best, but it still takes out a big bite out of the warmth of the guitar. I also own a ParaDI and have found that the notch filter on this helps, but still at a high cost to the warmth of the sound. Generally I've got around it by judiscious damping with the heel of my pickin hand - but its not ideal.

Now I wish to amplify a 30yo Maton acoustic guitar for use on stage and I'm keen to get a rich warm sound, but avoid these feedback issues. I'm happy to drill a few small holes in the old girl, but won't be cutting a hole in her side for a pre-amp. From what I gather, either the Anthem or the M80 are the way to go for a rich warm acoustic sound, and are purported to provide a significant improvement in feedback resistance.

The Anthem sounds to me to have a slightly richer sound (this is expected given that it is a mic, rather than a magnetic PU), but what I don't understand is why, with the cross-over is set to 250k (around the open B string), I wouldn't continue to have the same feedback problems as before. ie. the bridge piezo is still in charge of the frequency where it gives me problems with my other guitars.

I like the minimal interference to the instrument of the M80 - but I'll go with the richer tone of the Anthem if it isn't going to feedback at high stage volumes.

Is the M80 less likely to feedback at higher stage volumes that the anthem?
Is it normal for acoustic guitars to be vulnerable to feedback from lower G to lower B?
Have I missed something obvious in the feedback resistance of the saddle piezo pick-ups in my other guitars?

Please excuse the tome