I'd go with the refurb Sundown. They are the only one of the lot that is super reliable and if db-r repaired it, odds are he strengthened a few things while he was in there in addition to just fixing whatever was wrong.
I too have had a good experience with Crescendo customer service and wouldn't hesitate to buy their stuff again if it fit my needs/budget.
Strapping 2 amps to a 1 ohm load each amp "sees" .5 ohm. You will want a little more electrical for that probably. Also I'd run one amp per sub if that's an option over strapping (if you even go that way). I've done a lot of playing around and it seems they do better that way generally.