Its quite scary actually, as I compare both the PK1 and the M2C sitting here at my desk. If I flip the bass boost switch on my Fiio E10, the PK1 distorts heavily and sounds overblown, where as the Blox just gets more bass deepness. I feel comfortable saying the PK1 and the Charm are the most similar. Both are 150ohm and require a ton of power to drive properly, once you get that power the stage does open up in deepness and dynamics, but even then the Bass is anemic and easily overdriven. Both the PK1 and the Charm have a slightly dark, muffled experience with a wider than tall, distant sound, the Charm just has more bass and a bit less clarity.
If you really like the PK1, you are going to love the Hisound Paa1 Pro, its basically the PK1 on massive amounts of steroids. Its fun, well colored, more clear, more dynamic, more spacious and has a ton more bass yet its only $49. Sell your pk1 and buy a Live for your reference listening and the Pro for your fun time