What is Floyd Toole saying about extra amplifier power and headroom?

 I run XLR cables to my sub because when I've run RCA, there's a low-level hum from the sub that completely goes away when I use XLR cables.

DBX makes a DSP unit that has XLR outputs. https://dbxpro.com/en/products/driverack-pa2 If you shop around I think you can find one around the same price point as a MIniDSP.

Inline RCA active crossover? They make high pass filters for 70hz and 100hz. Any reason why these wouldn’t work?

These would work provided the crossover point the you need is either 70 or 100 Hz and they give you the proper slope. A DSP unit will give you many more crossover point options and should offer several different slopes.

@noble100 
Hi Tim, I do not have any actual experience with the MiniDSP. My experience is with DBX and XTA and both of those allow you to configure the outputs in any manner that you desire, From what I have read and heard, I'm assuming that the MiniDSP works the same way.

@diamonddupree Here is a post that is related to your original question.

https://www.whatsbestforum.com/threads/coda-no-16-amplifier.31078/page-2 (post #22).

I am interested in the same amp as this guy. It looks like this guy will have 2 amps to compare side-by-side in January. Here is what he is referring to on V1 and V3.

V1:
150 Watts x 2 into 8 Ohms
300 Watts x 2 into 4 Ohms
600 Watts x 2 into 2 Ohms
Class A ~18 Watts

V2:
250 Watts x 2 into 8 Ohms
500 Watts x 2 into 4 Ohms
1000 Watts x 2 into 2 Ohms
Class A ~12 Watts

V3:
400 Watts x 2 into 8 Ohms
800 Watts x 2 into 4 Ohms
1600 Watts x 2 into 2 Ohms
Class A ~8 Watts

Thanks @audiorusty, there seems to be no shortage of RCA crossovers and XLR crossovers but not many that have both. The only ones I've found are by JL Audio and SPL and both are fairly pricey. The DBX seems to be XLR only unless there's one I'm missing. 

I'm so glad I posted this thread because I've learned a ton. (You're not the only one @larry5729! Thank you @erik_squires @mapman @onhwy61 @mrdecibel @noble100 @yyzsantabarbara and everyone else!)

I have about an hour of listening with the MiniDSP. The setup was straightforward enough. I set the high pass filter for the mains at 90hz and the sub low pass at the same. The sub has its own LPF. The HPF I had to set using the MiniDSP software installed on my Mac. Once I had the software synced with the unit, which took about five seconds, I was able to set the high pass. Couldn't have been easier. I'll have to play around with the crossover point but a few observations so far. 

The amp is obviously not working as hard as before. I can reach the same SPL at a lower volume on the DAC (which doubles as my preamp). With the JL sub going up to 90hz, the bass is tighter and more finely detailed. I've been listening to an album called Wood by Brian Bromberg. He plays a 300-year old double bass with a lot of slapping, sliding and plucking techniques, which gives you a good taste of transient detail and the excellent character of the 18th century bass. There's a lot of it with the JL going up to 90hz and with the Magico Minis rolling off earlier. And there was a lot of detail already there before. But now, it's even more three-dimensional. It's the same thing with a Charlie Haden/Jim Hall album that's been on heavy rotation, where the bass articulation just jumps out of the soundstage.

I'm not sure if it's the mains not having to extend down to 40hz or the extra headroom from the amp not having to drive the mains that low, or maybe a combination of the two, but the DSP makes both the sub and the mains sound better, and the whole system more resolving. Brad Mehldau's piano from a 1990 Art of the Trio live recording sounds slightly smaller than another Art of the Trio recording from 1997, and both pianos sound smaller than Chick Corea's on Trilogy 2. I've listened to all three albums many times and never noticed the difference in the apparent size of the piano. Quite an upgrade for just a $200 piece of gear.

I guess I should just be happy at that but of course, I have reservations about the conversion going on inside the MiniDSP, which seems to make my DAC an afterthought. I'm really curious how an analog crossover would work but for now, I'm going to enjoy the improvements this inexpensive little upgrade has given me. Thanks again to everyone who took the time to respond and share their expertise. 

@yyzsantabarbara this goes back to my original question which is why does Floyd Toole, who obviously knows a few things, discount the value of headroom? It seems to help in so many scenarios but unfortunately, he doesn’t elaborate on it. LMK how the amp works out. I’m curious to know. 

Actually @audiorusty, I think the DBX would work. I could run XLRs from the DAC to the XLR inputs and run all XLRs out to my amp and sub. Thanks, this may be a better analog option instead of the DSP.