How to connect C2500, MC501 and Two Subs

Use the same taps you're using to drive your speakers. There are no 8 ohm taps? My understanding is that the high level inputs to your sub don't draw any power, it's just used for the signal.

I've got a MC452 driving two REL s510s. REL recommends using the high level inputs, so I used the REL supplied high level input cables (with neutrik speakon connectors on the sub ends). I used the 8ohm tap (same as my speakers).

The supplied cables are VERY long, and a bit cheesy, so I ordered a single Canare 4S11 with 4 spades at either end (at twice the length I needed) from Blue Jeans. When it arrived, I cut it in half and attached two neutrik speakon connectors I got from parts express to the freshly cut ends. Somewhere around $130 total and 30 minutes of work (only 3 of the 4 wires are used).

With the RELs you need to be a little careful connecting to your quad balanced amps as the negative terminals are "above ground". The ground wires to the sub need to go to your amp's chassis, not the negative taps. Not sure if the SVS SB-1000 needs the same caution or if it can use the speakon connectors.

You could also just use RCAs or XLRs from your preamp. 

"They" say the best integration of subs with your main speakers are obtained by using high level inputs. The signal to your sub is the same as to your speakers, having gone through the same signal path.

Maybe somebody else can support or refute this. I do know that manufacturers would not incur the added cost of high level inputs on the higher end subs without a justification.

I would guess XLRs would be the next best path, RCA last. 

In this hobby there will always be those that vehemently advocate or refute damn near anything without evidence, so make your own judgements and don't look back.

I use the high level inputs on my RELs, and am very satisfied with the results. Would I be just as satisfied with using XLRs? probably.