SQ? I can't really say since I haven't compared it to a different receiver of the SAME wattage. If I remember correctly, the 507 is 75watts/ch. It's probably ok for satellites.
I replaced it with a denon 1910 which to me, sounded "cleaner/softer" to the ear and had more impact/punch than the 507. Probably due to the higher wattage.
the 507 is not comparale to the 1910 actually as 1910 is already in the middle of the pack, this is actually pitted agains 606/607 and yammy 663, the four more or less have the same features wiht plus or minueses over the other
for a starter, the 507 is not a bad receiver specially if your not into those upscaling thing, even using floor staders or bs, the 507 will not dissapoint, you just need to get speakers that has a higehr sensitivity, atleast the way i understood thing as people are saying 90db sensitivity are easiser to drive( iwould have to leave response to further query on this to our HT gurus as as i can not go deeper in the explanation anymore). if your room is not that big and is working on a budget, then 507 is the way to go but if you have an extra juice to extract, you may want to consider the 606, 607 price range is from around 30k to 32 k perhaps. the post above for sale the 605 is actaully a very good option,the 507 would only cost as much. by the way, if you will try to reaserach, you would see that the Onkyo605 is one of the most sough after eceiver when it was relased getting 5 start rating and product of the year award from hat hifi magazine. you might want to pm or call the seller and give it an audition.
good luck on yor hunt