Prologic IIx is pretty much the only way to get 7.1 sound out of a 5.1 signal on most receivers. Some receivers will do DTS Neo:6 as well, but that only gives 6.1 sound (both back speakers would have the same signal in a 7.1 situation). [What about Logic7?]
Depending on your receiver, you may or may not be able to apply PLIIx to all 5.1 sources. For example, I cannot use (on my Pioneer VSX-816) PLIIx for multi-channel analog sources, DTS 96/24 or PCM 96 sources. More expensive (with more powerful CPUs) may have better luck in these situations.
Depending on your receiver, you may or may not be able to apply PLIIx to all 5.1 sources. For example, I cannot use (on my Pioneer VSX-816) PLIIx for multi-channel analog sources, DTS 96/24 or PCM 96 sources. More expensive (with more powerful CPUs) may have better luck in these situations.