My second Rumble 500 Combo finally showed up yesterday afternoon. I just got done testing the "Rumble Stack" plan and it is a roaring success. I vertically stacked 2 Rumble 500 Combos and it sounds glorious! All I had to do to link them was run the effects send of one to the effects return of the other and they work perfectly in sync from the pre amp controls of the master amp. The volume is the same and there is no buzz or ground loop noise at all. The advantages here are numerous as I see it vs a combo+extension cab setup:
1. Total Redundancy in case of amp failure at a show
2. More headroom. 700 watts into 4 10 inch drivers vs 500.
3. Lighter. The Rumble 500 combo actually weighs a few lbs less than the 2x10 extension cab.
4. Geo Diverse. Leave one at home and one at the practice space. Combine for gigs.
Obviously the downside is cost, but I got these for $417 each shipped from Sam Ash off of reverb.com so I only have about $100 more invested than I would in a combo+ 2x10 cab setup. Obligatory pic: