I have both the K702 and the X-Can V8p. The K702 is not everyone's cup of tea. I think you need to know that going in. The X-Can V8 is a fine headphone amp with plenty of power and a pleasant tonal balance. It's also pretty handy to have both the DAC on board and line input and output. All in all, it's a pretty handy piece of gear to have around, since it can actually be used as a pre-amp if necessary. As a building block to a future system, that's pretty cool.
What is it that you don't like about the sound? If you feel like it's missing bass punch, that's just the 702. It's not a super exciting headphone; it excels at neutrality, detail and, after break-in, a very nice smoothness. For comparison, my AKG K240 and Audio-Technica ATH-W1000 are both more exciting sounding. The W1000, in particular, is way more forward, but not as smooth or open. The K240 is slightly punchier in the mid-bass but less resolving.
What is it that you don't like about the sound? If you feel like it's missing bass punch, that's just the 702. It's not a super exciting headphone; it excels at neutrality, detail and, after break-in, a very nice smoothness. For comparison, my AKG K240 and Audio-Technica ATH-W1000 are both more exciting sounding. The W1000, in particular, is way more forward, but not as smooth or open. The K240 is slightly punchier in the mid-bass but less resolving.