My upgrades came from Jerred at Jolida in MD and they may be like those which (via Canada's "Parts Connexion") Underwood provides although I have no idea, but they seem similar in description. I use it with a beefy dual mono (Vincent-esque...same factory but the Kavent line is no longer around) Kavent S-33 preamp with balanced outs. Although the Jolida inputs aren't "truly" balanced, I like the solidity of the balanced jacks and I had some great balanced cables so I wanted to keep using them. My speakers are Silverline Preludes and a REL Q150e sub.