The biggest issue with the LG and a headphone like the TH900 is noise.
I love the LG to bits (I wanna kiss it on the lips). However it's just not the best option for extremely sensitive, low impedance headphones. The gain is determined by the tubes because that's just the nature of the beast. On most tubes I've tried, there's hum with very sensitive headphones.
I've talked to Alex about possibly getting an impedance adapter made.
The ZDSE however is a much quieter amp for extremely sensitive headphones. If you're not bothered by hum then it's no big deal. I'm really anal about that kind of thing however, so I don't use the LG for those types of headphones.
I see. Despite being a tube amp, the ZDSE is dead silent with my TH900 without any audible hum or background noise. I have to admit, it does sound more tube-like than my Soloist (whose clarity is unmatched), but the massive soundstage it throws over the two closed cans of the TH900 is just pure bliss. Tube rolling from stock Tung-Sol 6SL7 to 50's-made Mullard ECC35 made a significant improvement too.
Stefan AudioArt has recently upgraded its umbilical power cable for the ZDSE and it's on my way. With that my end-game headphone system will be complete.