SMSL 98E killed my setup?

So today I got the SMSL SA-98E amp from amazon after waiting for 50 days. I was pretty excited since I could finally test out my new passive speakers. My setup up to then was a scarlet solo and a jds atom amp to drive my HD600s. So I unplugged my headphones, connected the rca outputs from the atom into the rca inputs of the smsl, and hooked the speakers to the smsl. When I tried to play music, the speakers made a high pitched buzzing sound not too different from a sine wave, and there was no hearable trace of the music I was trying to play. I started troubleshooting, rechecking the speaker cables were connected properly etc. I noticed that the buzz became much quieter when I unplugged the rca inputs of the smsl, and upon reconnecting said inputs, the speakers made a very loud sound like when you touch a live guitar cable; I immediately turned the smsl off, but the atom amp and the scarlet solo didn't survive the ordeal. Their lights were off and they showed no sings of life. Since then, my atom amp has turned back on but it outputs an
obnoxious sound like the one that came out of my speakers, even without any input at all, and my scarlet solo hasn't turned back on.
Have I killed my scarlet solo and atom amp? If so, was it something I did wrong with the wiring or can plugging a defective amp kill other components through rca?
Any help appreciated

Unless your integrated can be reconfigured to be used as just a pre or just an amp with the use of jumpers or a bypass switch,it's not possible to plug in an outbourd pre.The inputs are only for source components.
@djones51 I think this is what happened, I certainly didn't unpress the gain button, and looking at the atom manual, it specifies the use of low gain when using it with speakers. 
So from what I understand my setup could work as long as I change the gain button on the atom every time I want to use the speakers? That seems pretty risky if I can fry 200$ worth of equipment at the press of a button or lack of thereof.
@dill : You can connect a preamp into another preamp. Just keep the volume control low so you don't overdrive preamp #2. 
So I had no idea that the smsl had a preamp and a power amp.
Audio can be very confusing, so thank you for clearing things up.
From what I understand, the impedance mismatch made the signal backfire into the amp and scarlet, frying them both.
I think I'm going to get a new atom amp and scarlet solo, since I need the microphone input, and I was happy with my atom amp. If I understood correctly, I would need a new power amp to make the speakers work.
Do you have any recommendations for a power amp around 100$? Otherwise, how do I ensure the new amp I'm getting doesn't also have a preamp?

@jtcf : See my above post.