Is the m6si really that much better than the m5si?
I would say somewhat. It will have the same general sonic signature. And you are not buying the M6si to use all 220 watts. You buy the larger amp because a larger power supply will generally have more "oomph" in the bass/midbass area and also usually be smoother and fuller in the midrange (even at lower volumes). If you can afford it, go for it. Otherwise, buy what your budget will allow.
The Parasound Halo integrated is nice. Think of it as a swiss army knife type of device with every feature you could imagine. However, the individual features (DAC, phono stage, etc.) are just average/mediocore. If you need all the features, great. Otherwise, there are better external DACs/phono/etc. The Parasound are voiced just slightly to the warm side of neutral. Very smooth, but the high frequencies are slightly rolled off and softened (maybe closer to the Marantz 8005 sound, but I can't be sure because I have never heard the 8005 directly). The Music Fidelity will probably have a lot more attack than either.
The Parasound Halo integrated is nice. Think of it as a swiss army knife type of device with every feature you could imagine. However, the individual features (DAC, phono stage, etc.) are just average/mediocore. If you need all the features, great. Otherwise, there are better external DACs/phono/etc. The Parasound are voiced just slightly to the warm side of neutral. Very smooth, but the high frequencies are slightly rolled off and softened (maybe closer to the Marantz 8005 sound, but I can't be sure because I have never heard the 8005 directly). The Music Fidelity will probably have a lot more attack than either.