I did it successfully, using these instructions:

Replace cassette

Hi everyone, Just bought an 07 Touring and I love it. I was getting tired of the expense of fueling my Tundra and then my buddy fell asleep and totaled it! Insurance paid $2K more than I paid for the Tundra. So now I drive the Avalon. I have always wanted leather and lumbar support. I didn't...

www.toyotanation.com

inov8 has an awesome and relevant tutorial linked there, for removing the center console. The link is dead, but... The Wayback Machine comes to the rescue:

Wayback Machine

EDIT: Is your Sony head unit an XAV-AX5000 series? Good choice. I installed the AX5500 in my 07 Avalon and I was really impressed. I'm pretty sure I'm going with Sony head units for the time being. They look near-OEM in the Avalon at least, and the interface seems a bit more "professional" and less goofy-aftermarket like the several Kenwood and Pioneer midrange double-DIN units I've owned over the years. Pioneer and Kenwood do make some good head units, but I've yet to own one that I liked more than the AX5500 and the much older AX100.

 

Thanks for the info and links! I will attempt the exchange as soon as I have some free time.

Ha! I installed the Sony 5500 as well. Used the

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PAC RP4.2-TY11 Wiring Interface to retain steering wheel controls, factory HVAC controls and dash info display. I also installed a backup camera viewable on the Sony.​

Replaced the door speakers with 2.3ohm JBL GX628 speakers. They work great with the factory amp.

I just installed a kenwood mono amp under the driver’s seat, and the Infinity 1270b 12” subwoofer in the trunk. Not a basshead, just want depth in my music. And it is perfect!! I disabled the factory subwoofer even though it still works.

 

WHY would you do this!? You can Blutth the sound. And I actually have cassettes . YA young wipper snappers! Seriously though..... blutoth

 

Video on how to remove the center console of 05-12 Avalon. It’s for installing a bluetooth module, but also useful for accessing the tape deck ( see 2:20 to 3:20)