Reddit mentions of Pyle Home PIDOCK1 Universal iPod/iPhone Docking Station for Audio Output, Charging, Sync with iTunes and Remote Control

That's actually a pretty big pavilion. I'd go rent some PA speakers and a real amp. Five little wifi speakers aren't going to work for a pavilion like that with more than a dozen people in it.

As far as connecting an iPod to the amplifier, I'd go with a dock that has an unamplified stereo output (something like this). If you want to go wireless, use a bluetooth receiver instead. Either option will work with any standard amplifier that you can rent.

FWIW I used to DJ in clubs and did a couple of weddings as well. It's easy to underestimate how loud those events get and how much power you actually need for a sound system. Better to have too much than not enough.

http://www.amazon.com/Apple-MC746LL-A-Universal-Dock/dp/B0019FMEO0/ref=pd_sim_sbs_e_2?ie=UTF8&refRID=1T2A5ZE08NNYMCJHQ4X1#productDetails

http://www.amazon.com/Pyle-PIDOCK1-Universal-Docking-Charging/dp/B0056IB3DY

I don't own the BX5, but i'm guessing it has 1/4" jacks so you should be good with that.

Only pain is going to be controlling the volume, you will have to do it from the input device. (BX5, similar to the KRK monitors I own, have volume control per speaker on the back, which makes it inconvenient to adjust)

I personally have never used this, but it might be worth trying -
http://www.amazon.com/Scosche-RLC-Remote-Level-Control/dp/B002EEP3WA/ref=sr_1_18?ie=UTF8&qid=1369926618&sr=8-18&keywords=volume+control
(I just searched for volume control, or line level volume control)
http://www.amazon.com/TC-780LC-Stereo-Booster-BLACK-VERSION/dp/B000RZXAHI/ref=sr_1_7?s=electronics&ie=UTF8&qid=1369926740&sr=1-7&keywords=line+level+volume+control this might be cool, don't really know.

you will then need http://www.amazon.com/Hosa-Cable-CPR202-Dual-Inch/dp/B000068O17/ref=sr_1_2?ie=UTF8&qid=1369926629&sr=8-2&keywords=RCA+to+1+4

There is also some cables for iphones that output rca. Things might be different now, but if I remember correctly the way the sound was routed to the headphone jack was actually different than the output from the apple connector thingy.

You might be able to find a iphone dock that has RCA output and volume control. I saw this one http://www.amazon.com/Pyle-PIDOCK1-Universal-Docking-Charging/dp/B0056IB3DY/ref=sr_1_9?ie=UTF8&qid=1369927022&sr=8-9&keywords=iphone+dock+rca looks kinda crappy though.

volume coming out of your normal PC sound card will probably sound fine. A cheap (sub $20) usb soundcard might make all the difference if your soundcard isn't so hot.

1. iPod Dock
   
   
   
2. 3.5mm to RCA
   
   
3. Bluetooth adapter
   
   
4. Chromecast + HDMI to HDMI with analog audio output + 3.5mm to RCA Standard RCA cables (L/R)