Anybody know what happened at JOB...

In my 1/2 dozen times of hearing the RX20s, I always preferred ss amplifiers with  well designed, beefy, power supplies. Some were 40 or so wpc, some were 200 wpc. The speakers are a nominal 8 ohm load, so it should not be a problem for the STA 200. What I feel would be amazing : what I suggested to Abery. To vertically, passively, biamp them, which would require a pair of amps, and at a grand, would be killing a few stones, simultaneously ( read up on this amp configuration set up ). As Abery indicated, and as mentioned before on other STA 200 threads and reviews, matching, to the front end gear, can be tricky. Enjoy ! MrD.

My zus are super efficient. I have a BHK pre that has tubes. The gain of the Nuforce is do high, I had to install a passive pre between the pre and amp due to tube hiss levels. I reality I have the wrong amp for my speakers (101 dB efficient- at least that is what is advertised). I would say the Nuforce is a perfect amp for speakers under 94 dB or so. 

I got my STA200 a few days ago. Driving Klipsch RP600m speakers, The source an Oppo 205 and pre a terrific little McCormack Micro Line Drive and an alternative pre, a Placette Passive linestage. The sound was superb. This despite a far less than ideal acoustic space. I did experience a loud hum, but bringing the system to another room eliminated that.
From comments above it would seem that the Job 225 is not really better, just more powerful?

abery, I have to disagree with you, my friend. You had the Rogue pre, prior to your BHK, and you needed to do the same with the Schiit passive. The problem is not with the Nuforce and Zu interface, but the pre’s and the Nuforce. If you eliminate the pre’s, and go passive, without signal playing, turning the passive volume up to max, you would not get hiss or hum ( if no grounding / wiring issues ). It is fine if you want to change the amp, but I remember mentioning a long time ago, the Nuforce, and Job 225, were designed to be driven passively. My Luminous passive ( awesome ), at max volume, without music playing ( dac is on ) shows zero hiss, or hum, through my more efficient speakers, when using the Nuforce. But I understand how much you enjoy tube preamps, so the Nuforce is not a good match, interfacing with your preamps.

adameos, in your 1st room, when you experienced the hum, might be because of a severe ground loop, or even a light dimmer, on the same circuit. Could be any number of things. But the amp is quiet, when used with better matched components, preceding it, in the audio chain.