theaterdoc,
Brain physiology and home theatre hookups. In essence they are both electrical devices wired in many ways.
In light of that thought, you should be more qualified in home theatre than anyone here no?
Both the Onkyo and the Denon brands are good choices for a home theatre integrated receiver. They tend to incorporate the most common requirements for playback of today's dvds (Dolby Digital EX, DTS, multiple speaker hookups, etc.) while providing a wide range of prices and options for any level of consumer.
I personally have an Onkyo DS797 (last year's model), and could not be happier with its performance.
That being said, i do not have the M80s, i have M60s (a 4 ohm speaker vs. the M60- an 8 ohm speaker).
There has been a fair bit of debate over the power handling capabilities of several common receivers. Many of them do not carry specifications from the parent company on supporting 4 ohm speakers. However, some receivers will still successfully and easily power speakers with a low impedance. Sushi recently bought an expensive Pioneer receiver which seems to be working out just fine and i have used my Onkyo DS797 with 4 ohm speakers without any issues. Others have reported problems in this regard albeit with different models (the Onkyo DS787 comes to mind) or brands (some Harmon Kardons offhand) of receivers. You will want to check out the ability of these receivers to power a 4 ohm speaker properly before putting down any cash.
Be sure that you get a solid answer from someone who has already tried the M80s with the two receivers you are interested in before you commit to your purchase unless the company specifically gives you a specification for running speakers under 8 ohms. The last thing you want to have is a new receiver that starts billowing smoke or constantly shuts itself off because the M80s are too much for the unit. Warranties often do not cover such 'abuse'.
As for the THX thing, again, people debate it. THX certification (especially the Ultra categories) do go through some rigorous tests set forth by the THX specifications. However, if a unit is not THX certified, it certainly does not mean it's not up to the task of performing. Many expensive units/companies do not even bother with such certifications because their components sell without it (usually due to quality but often also due to reputation).
Your setup selection otherwise looks great. Personally i'm not 100% sold on the performance of my EP350 but certainly the system as a whole is superb for home theatre while surprisingly revealing for music and incredibly accurate for its cost.
