If you are looking for something more neutral at around 350 I highly recommend the Sundara. That’s the way I went from my 770 and I am impressed. You can find my detail thoughts in the Sundara thread here 
HiFiMan Sundara 4th post from the bottom can’t miss it 
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It will probably work ok with the smsl for now but you will really want something more powerful in the future. I am driving them with my Liquid Spark and they work very well together.