This Hosa CMP-153 (3.5mm to Dual 1/4' mono plug) cable, $5.99, will connect the E10K to the Monoprice studio monitors.http://www.sweetwater.com/store/detail/CMP153 Later on you can easily integrate the Monoprice sub-woofer with the Monoprice studio monitors.
The Vali has an output impedance for 6.5-Ohms, so it should work decently well with all your current headphones (even the SE215).And you always have the option of plugging headphones directly into the E10K amp.So i say get the Vali (your K7XX will thank you for it)
A FiiO E10K would make a better DAC for the speakers (studio monitors) and headphone amplifier, for your headphones. Here are some great studio monitors for $171 (I've been using them for the past year).http://www.monoprice.com/Product?c_id=115&cp_id=11504&cs_id=1150401&p_id=605500&seq=1&format=2
You really can't create a lot of bass from a headphone that is not really bassy in the first place.Or you try so hard that you end up with a bloated (louder and less detailed) bass.You might consider taking the time and find a good price on a used Philips Fidelio.