If it helps at all, I've got the G6 and use it with a JDS Labs Atom headphone amp, and I noticed a difference in sound quality between that and using the headphone amplifier built into the G6. I wanted to get the best possible audio experience from my headphones though, so whether or not you go with the L30 depends on how much you prioritise sound quality. Also I would recommend you just use your G6 with the L30 rather than buying another DAC unless you want the features of the E30 like remote control & some of the other features. Re using your G6 with the L30, make sure you run Windows Volume no higher than 85% as that equates to -2.4dBFS, and the G6 shows distortion above -2.0 dBFS according to Amir's review of the G6. The G6 has excellent measurements if you run it below -2.0 dBFS:
https://www.audiosciencereview.com/...w-and-measurements-of-sound-blasterx-g6.7016/
(You would of course attach the Line Out port of the G6 to the L30, you wouldn't attach it through the headphone port on the G6, but you know that!)