We reviewed them head-to-head in a Group Test for our October 2007 issue. The Pioneer got four stars to the Onkyo's five, with it falling short of the latter with both movie and music performance.
The VSXLX70 is feature-packed receiver that sounds powerful and exciting, but we criticised it for some high-frequency stridency and lack of detail (the latter being particularly apparant with music). It's got a horrid remote, too (if such things matter to you).
The Onkyo is second only to Arcam's AVR280 in that test for music performance, though leagues ahead for movies (the Arcam got a three-star rating - it's still the most musical receiver, but is way off the pace for cinema sound now). We described the Onkyo (which we later gave an Award to in its price class) as delivering "a natural, uncoloured stereo sound that's well focused and well judged". Anything against the Onk? It runs hot - so you'll need plenty of room on your kit rack - and it's not the best-looking.