one of the goals in my desire to upgrade my preamp was to be able to adjust the audyssey curves for the mid frequencies (mainly to compensate for the usual hearing loss). If I am able to connect some type of equalizer to the preamp could I accomplish the same goal?
Yes you can use for example a minidsp device. You are right about the ability to adjust the target curve if you go with for example a Denon or Marantz AVR that comes with XT32/SubEQ HT.
You can also go with Yamaha that comes equipped with YPAO. There are also Anthem ARC and some comes equipped with Dirac Live. So it all depends on your budget. All of those would give you the ability to manual tweaking after running auto setup.
You thread title is about Audyssey App vs PEQ, it is obviously not an apples to apples comparison but you may want to read minidsp's comparison on FIR vs IIR. Audyssey is FIR based, PEQ is sort of IIR based:
FIR vs IIR filtering (minidsp.com)
Other than that I would say the Audyssey App may be a little easier to use if you use it with a third party user interface called Ratubuddyssey, that allows you to enter the tweaks you want to make at the frequencies of your choice, such as +2 dB at 2000 Hz, -3 dB at 250 Hz etc., whereas with PEQ you have to know how to calculate the "Q".
