Nuforce STA200 hum noise, will a preamp solve it?

Like a few others here, I am somewhat of a HiFi novice as well, so please bear with me if I don't understand some of the basic principles or expectations.

I just purchased a new STA200 thru Amazon for the discounted price of $499. I had read about the gain sensitivity, but thought that maybe my 'bare bones' system configuration would mollify any potential noise amplified by the amp.

My basic system is: Jolida Glass FX DAC > STA200 > KEF LS50s w/ Morrow MA-3s connecting the DAC to the amp and Morrow ST-4s connecting the amp to the speakers.

When I connect the speakers to the amp and turn the amp on ... its' dead silent. When I connect the ICs to the inputs on the amp, but do not connect them to the DAC or anything else, and turn the amp on, there is a hum noise ... not real loud, but definitely there. When I connect the Jolida to the other ends of the ICs and turn the amp on, the hum remains, but the volume level of the hum is pretty low. The sound, from the music (either CD's from a Rotel ACD-1072, connected to the DAC with a Kimber D-60 Illuminations coax, or from my PC to the DAC connected with an AudioQuest Coffee USB cable and the PC running FLAC files through Foobar) is fantastic and the hum can almost be ignored, except during quiet passage in the music ...but the hum is still there nonetheless. Another interesting effect, is that the volume of the hum increases as I increase the volume on the DAC (after disconnecting all inputs into the DAC, of course) until I get to the upper range on the volume control .. then the volume of the hum drops way down. It doesn't disappear, but it is fairly quiet.

I was hoping to save a few bucks in the short-term and not have to buy a preamp (and the spring for cost of additional IC cables to connect everything) right away. However, I would be willing to invest in a preamp (as well the additional IC cabling required) as long as the hum goes away and there is no background noise once the preamp is connected into the system. I've been researching the HAP-100, Schiit and Rogue preamps.

Does anyone know if the hum will go away if I connect the DAC through a preamp? Or is there another problem I am not addressing? (that's why I started with only amp & speakers connected, to make sure it was dead quiet ... no poor connectivity or power problems). If the hum is coming through the DAC, then it seems that a preamp maybe won't solve the problem ... or will it? (i.e. the louder hum when there is nothing connected to the input cables and yet is dead quiet when there's no input cables connected at all). Or do all 'reference-level' systems produce a bit of hum?

I've really enjoyed being a member here at Audiogon and respect everyone's insights, observations and suggestions and I'd really appreciate any advice that any of you could provide.

    I'm sure it's disconcerting to hear a hum in what should be a very quiet piece of gear. I'm considering buying one of the same amps for my office system. When convenient, try switching off every circuit in the house at the breaker except the amp. If it's quiet then you have a bad power supply in a lamp, computer, or some other device. We once had a computer with a in-line power supply that transmitted so much radio frequency energy that I'm surprised that the neighbors didn't turn us into the FCC. By turning the circuits back on, one-by-one, you will be able to find the offending device.
    Then make sure that all of your equipment is properly grounded and that their are no ground loops. You could try lifting the ground with a cheater plug; if that helps then you may want to more deeply investigate ground loops and how to solve them. Various AC line conditioning could help but they can get extremely expensive.
    I don't think the issue os related to a lack of a pre-amp.

 When I connect the ICs to the inputs on the amp, but do not connect them to the DAC or anything else, and turn the amp on, there is a hum
noise ..

This sounds like induced EM noise. It is caused by running the IC's too close to a large current source or transformer. The transformer is the part of gear that lowers the incoming AC voltage, so you may want to try placing your amp elsewhere physically to reduce the proximity. 
Thank you for responding to my question. You both make a good point of some EM interference being generated from something that is probably causing the noise. I do know that when I first set it up, there was another noise in the system which disappeared after I turned off the small space heater in the room. So maybe there is some other source of the noise which I have not yet account for.

The curious thing is that the humming noise increases as I increase the volume on the DAC (the Jolida Glass FX has a headphone amp which I'm using as a preamp) until the volume on the DAC gets to about 80% of full volume. Then, the humming sound coming from the speakers decreases as the volume knob on the DAC is turned higher until at about 95% of full volume, the hum noise is gone and the system stays dead quiet all the way up to full volume. I guess I thought that, if I had a preamp, I could run the DAC at near full volume and regulate the volume coming through the system to listenable levels using the preamp. But this gets more complicated and certainly more expensive ... and it may just be wishful thinking. And I would probably still have the errant EM source that I would have to eliminate one day anyway. So I will try and find the source of the hum as you have suggested and try to solve it that way.

Thank you very much.