I have the Outlaw Audio LFM-1 EX (rebranded HSU with a BASH amp). I contacted tech support and they claim that the high level speaker inputs handle these amps. So, I hooked it up, closed my eyes, and flicked on the power. Kaaboooommm!!! Just kidding. Nothing happened and it seems to work fine. Note that I only attached the left channel from the power amp to the left channel speaker-level input of the sub. My sub's speaker level inputs are designed for 100 - 200w so the DDA-100 produces a pretty attenuated input to the sub's amp. I had to double the volume of the sub to trim it up into the range of the mains.
The DDA-100 is a fun amp to listen to music on. It has great texture and detail especially through the mids. The location queues are also good as is the separation. The USB input isn't async however so it depends on how jitter free your source is. A lot of people are purchasing an async USB to SPDIF converter to remedy the situation. I think the USB input is engaging all the same. @ArnyK, I'm with you on the "tail wagging the dog". One review I read (The Absolute Sound) suggest buying a $1200 USB to SPDIF converter to go with this $550 amp and that's exactly what I thought.
Another option I considered was a speaker-level to line-level converter with an isolation transformer. These folks make a line-level isolation transformer (http://www.jensen-transformers.com/sub1rr.html
) as a way to de-couple a sub from the main system. This might also help for with those sub's that lack speaker-level inputs. I have an inquiry into Jensen Transformers on the topic. I'll report back when I hear from them.
As for the sound of the DDA-100, it's very nice for music. Great texture and detail through the mids. Sound stage is reasonably deep and layered. Location queues are good. Music sounds very natural and authentic. Stringed instruments and vocals particularly seem to stand out more so than the other amps I've got. I wish they would build a model with a larger power supply as I felt the 4 ohm speakers I was using seemed somewhat current-starved. This effects bass performance primarily and had to be augmented with the sub to reinforce the bottom end. The under-representation of bass in the upper-bass and lower-mid section may perhaps be the reason for the increased texture and detail in the mids that seem to favor some types of music so well. In short, I wouldn't recommend this amp with 4 ohm speakers without a sub. If I had some high efficiency 8 ohm speakers that were close to full range, it might be great though without a sub.
This reminds me of the Ongaku that I spent some time with a while back. (Review here: http://www.stereophile.com/ces2009/ongaku_means_ecstasy/index.html
) Specs on paper were bad. 3% of all the sound coming from this amp didn't match it's input but it sounded great. The DDA-100 is obviously not in the same league but I think it sounds good with music in my setup perhaps partially due to inappropriateness to my speakers in that it just reveals more midrange detail and texture as a result. The Ongaku on the other hand manged the VMPS speakers just fine and sounded great in spite of some pretty horrible looking numbers on the spec sheet.