Hello areasonableman,
The Class D Audio SDS-470C is a very good choice for a very good amp at a very reasonable price. It’s got plenty of power to drive the LRS, has balanced and unbalanced inputs and has an accurate and detailed presentation that I’d describe as very neutral; meaning it won’t add or subtract anything from the inputted signals.
I understand that, if you had the money, you’d prefer buying and using the class AB Schiit Vidar in stereo or monoblock amp form but I believe you’ll enjoy the LRS with the Class D Audio SDS-470C amp, too. Here’s a link to some info on the 470 amp:
https://classdaudio.com/sds-470c-class-d-audio-power-amplifier.html
I’m a big fan of class D amps and have used 3 of them to drive my Magnepan 2.7QRs over the past 5 years:
A Class D Audio SDS-440-CS stereo amp that currently drives a pair of rear surround speakers in my combo 2-ch music and HT system.
An Emerald Physics EM100.2-SE stereo amp that currently drives my center ch speaker in bridged mono configuration.
A pair of D-Sonic M3-600-M monoblocks that currently drive my 2.7s.
All of these are very good amps. However, I actually agree with you that the class AB Vidar may be a better choice in the long-run than the Class D Audio 470. The reason is the very high Damping Factor of class D amps in general that can be very high, in some cases greater than 1,000. The class AB Vidar has a damping factor of a relatively low 100.
Damping factor is a spec that measures how effective an amp is at controlling the movement of a speaker driver (starting and stopping it) or sound transducer such as a planar-magnetic panel. The higher the number, the more control an amp possesses and vice versa.
In my experience with all three class D amps, I’d describe their performance on my Magnepans as very good but I perceived the bass performance on them to be exceptionally good, in fact the best bass I had up to then experienced with the rather large 623 sq. inch planar-magnetic bass panel sections on my 3-way 2.7s. I considered the bass on all three as very powerful, detailed, dynamic, perhaps a bit exaggerated and overly taut initially but discovered soon after that these bass attributes were the result of the excessively high damping factors on my class D amps. Even though I admittedly enjoyed the sound of the bass, I soon discovered that the bass was exaggerated, truncated bass note decays and didn’t faithfully reproduce the bass contained on the recordings.
I only discovered this because I had the good fortune to purchase an Audio Kinesis DEBRA distributed bass array (DBA) system about 3 years ago. This consists of four 1’ x1’ x 2’ 44lb. subs with 10" long-throw aluminum woofers strategically placed in the room with all subs powered by a 1,000 watt class AB amp/control unit.
Once I installed and heard the DEBRA’s powerful, dynamic and detailed bass, that was not exaggerated and didn’t truncate bass note decays, I perceived the bass as more accurate, natural and understood that this system was more faithfully reproducing the bass contained on the recordings.
My intent of relating my experiences with class D amps is just to make you and others aware of this tendency with at least my class D amps to exaggerate the bass content. Other than this tendency, I really appreciate and enjoy the accurate and neutral presentation of my class D amps.
My intention is not to discourage you or anyone from trying or using good class D amps in their systems. As I’ve stated, I actually enjoyed the exaggerated bass on my Magnepans and I believe others might too. Perhaps the LRS could use a bit of a bass boost since they’re only rated to extend to 50 Hz. If you prefer more accurate bass, you may want to save up for the Vidar.
Here’s a REDDIT link to some comments on the Vidar’s relatively low damping factor of 100:
https://www.reddit.com/r/audiophile/comments/7nig0e/schiit_vidar_review_from_the_audiophool/#bottom-...
Here’s a link to another positive review on the Vidar:
https://positive-feedback.com/reviews/hardware-reviews/schiit-vidar-amplifier/
Tim