I just started demoing my LP and M1570 today. I'm sure YMMV depending on what kind of tubes you roll, but I've got a couple Brimar CV2494 tubes in mine. Compared to my Singxer SA-1, the LP+Brimars adds a little bit of air, little bit extra width, bass gets a little more energetic, but the biggest difference is that good ol' tube smoothness. I just adore the silkiness it adds to everything. It's especially apparent with brass instruments. And the M1570 is already a very natural, musical-sounding headphone to begin with, but even more so on the LP with these tubes.
I'm running balanced out of my Modius into the LP, and using a custom balanced cable to my M1570, so a fully balanced chain. I've got the knob at just 9 o'clock and it's already plenty loud. Monoprice advertise the M1570 as a 60-ohm headphone and the LP as outputting 4.21W at 56 ohms (balanced). So, ample amounts of power on tap, as well.
So far, I'm enjoying the combo. I still have some A/B'ing to do, but neither of my amps disappoint. And on my first listen, the LP seems to be a bit more enjoyable, even. I can't comment on performance with the stock tubes, because they're pretty universally regarded as being not-so-good, so I started tube rolling the instant I got it. So if you do pull the trigger and feel underwhelmed, the stock tubes are a likely culprit.