Mpeg2 is encoding, like mpeg4 is (xvid, divx, H.264, x264, etc)
Nagravision is encryption
QPSK/8PSK is modulation
All 3 are 100% different, nothing to do with each other the signal they send is Mpeg2 but they don't send 1's and 0's as that wouldn't work.
They need to transform that in a suitable analog waveform first so that signal, "normally" they take 2 bits from it, and transform that into one of 4 voltages (levels) that's quadrature (as in 4) phase shift keying (QPSK) 2 bits, = 4 states so for every symbol a transponder sends (usually 20 million symbols per second) that sends 2 bits so 40MBit per sec but, what if you want more to fit on there? That's where you move to other modulation types 8PSK is another one of them now you take 3 bits, and transform that into 8 levels (2^3 is 8) now you have 20M samples * 3 bits/sample, or 60MBit! BUT, normally, to be able to use that, you need a stronger signal or bigger dishes as with 8 levels, you only have half as much voltage between the different states so it has to have less noise/higher quality that's where the turbo part comes in which lets them use it, on the exact same equipment (no higher powered sat, no bigger dishes), with more error correction so they don't get quite 50% extra out of it, perhaps more like 35% but it's still 35% extra bandwidth, on the same sats and dishes 35% extra BW, out of a bird with 32 TPs, is like having an extra 11 transponders' worth of bandwidth all of a sudden so more channels, without launching new sats the 8psk module, is a 8PSK modulator, because the QPSK demodulator in normal boxes, have no idea wtf them 8 levels do that fancy 8PSK demod on the module, takes the 8 levels, and converts it back to 3 bits for each symbol which the QPSK would never be able to do.

That's why all the ppl that ask if it couldn't be done in software makes me laugh the QPSK demod chip can't even turn the damn 8PSK RF waveform/signal into 1's and 0's, i dunno what they expect the box to do with no data past 8 levels, we don't use phase shift keying anymore, but things like quadrature amplitude modulation e.g. 16QAM but then again, we'd need higher powered sats, or bigger dishes everywhere but one extra bit out of each symbol (4 instead of 3), so only 33% increase tops, and massive equipment swaps required.