I would have thought it better to choose a pedal designed to get the best from an acoustic guitar - as far as I know the HD300 is designed primarily for use with electric, and to simulate different electric guitar-specific amplifiers, although it will do some effects too. If you want Line 6 stuff then look at an M9 pedal, since that will give you the equivalent of lots of effects pedals in a single unit for true multi-effects. Also consider other acoustic-specific effects units from the other big manufacturers like Korg, Roland/Boss, Zoom, Digitech and Fishman. The Fishman units are more pro-quality than some of the others, and priced accordingly, but from the demos I've heard will sound better.
I think the best thing you can do for an acoustic is add some compression, delay, reverb and chorus. Sometimes it's nice to have a boost like a Fat Boost to make your flat picking and finger picking stand out. I have separate pedals for each and don't always use every one. Multi effects pedals are nice because you can create a patch for each song during the week and just punch in the patch for that song on Sunday.
But they're not all created equal and I find most of them to be more trouble than I'm willing to spend time fiddling with. You need to shell out some $$ to get one that's quiet and reliable. Fishman makes units that are very high fidelity and sound especially good on acoustic. But I don't think I'm missing anything in my setup either.
"I think the best thing you can do for an acoustic is replace it with a Strat".
with a valve amp
I use a Zoom A2. It does the job and is tough and reliable.
I use Boss pedals with my acoustic: Chorus, Digital Delay (very light), and lately my SD-1 Super Overdrive (set very lightly). People have commented that they really like the tone (I use a Yamaha LLX26C). I've found that the key is to not add too much, as the acoustic body just muddies things up. But with a light hand, you can find your different sounds and fills.
Sorry to the electric players, but after more than 40 years of playing acoustic, I just can't get the feel of leading with an electric! Wish I could; I'd love to do some lead but just never get the opportunity.
Better to use what works best in your hands than something that doesn't, Rick.
Brian - have a look at these 2:
The timeforce will also loop, although AFAIK there's no drum loops. You might also consider something like a Fender G-DEC amplifier, since that has a bunch of different effects, looping and rhythm patterns built in IIRC. I'm sure it also has a 'phones' out for direct to PA.
If you go Line 6 go for the 500 instead of the 300. Its worth the extra money for the flexibility. The M9 is not a bad suggestion but all of the M9 effects are also in the HD 500 and you can chain up to 8 at a time as opposed to 4. Separate pedals do sound better but the cost grows significantly. The HD 500 also has decent amp sims if you go direct. I have invested in a very good tube combo amp so I am only using my 500 as an effects unit at the moment but I have used it direct to the PA in the past.
If you can swing it..Fractal Audio Systems Axe FX...."macdaddy"
I understand the 'Ultra' model is a worthwhile upgrade, but the few I know who bought them still seem to find them good. However there's been a shift among guitar players toward Kemper type modelling units at the very top end of 'artificial amplifiers' in the circles I seem to float in, and the Axe FX seems to hardly get discussion at all now.
I'd like to try a Kemper, but it's another league away from my finance, abilities and requirements.