For $2,000, I can add a pair of Anthony Gallo TR-3D subwoofers which have both high and low level inputs.
Here are some articles written by Paul McGowan owner of PS Audio. Paul believes that high level inputs are the correct way to connect the subwoofer.
FEEDING A SUB:
HTTP://WWW.PSTRACKS.COM/PAULS-POSTS/FEEDING/7948/
GETTING BASS RIGHT:
Getting bass right | PS Audio
Here is the 10Audio review of the “Gallo Reference Strada Speakers and TR-3 Subwoofers”. Jerry uses a pair of Gallo TR-3 subwoofers with his $17,000 YG Acoustics Kipod monitors.
Gallo Reference Strada Speakers on 10 Audio
Near the bottom of the review Jerry says “The TR-3 subwoofer is a surprise. For about a grand each, I expected a subwoofer that offers good performance, especially with its 10 inch ceramic-enhanced aluminum cone driver and 300 Watt built-in amplifier. This expectation was partly due to the fact that Anthony Gallo is obviously a smart guy, a good speaker designer, and a good listener. He undoubtedly learned something with the previous TR-1 and TR-2 models. “Learned something” doesn’t begin to explain the truly outstanding musical performance of these subwoofers. Their speed and resolution, especially when used as a stereo pair, is exemplary. They combine the impact and fine detail of the $2,800 (each) JL Audio fathom f112 with the natural warmth and resonance of the $1,800 Velodyne Optimum-12.”
The TR-3 is now the TR-3D because it has a cool running Class D amplifier. When 10Audio reviewed the TR-3, Jerry said “The rear mounted amplifier can become warm and needs some ventilation”.