Hello everyone. I bought a 704TV on ebay with 1.7.17 installed. This is an initial OS version. Then I searched for deleted files on the drive and did a recovery of them. Thus I found a firmware file of 1.7.17. You will never find it on the Internet (actually it didn't appear at all) so here's the way for downgrade. Download a704TV_1.7.17.zip from the link below. Unpack with "right click->winzip(winrar, etc)->extract to folder 'a704TV_1.7.17'". Remove the hard drive from 704TV and connect it to PC directly or using some IDE-SATA, IDE-USB etc converter. Use "HDclone" from this file http://www.4shared.com/zip/mC4Yq3THce/WD_Firm.html
How to unpack the program: the main archive file WD_Firm.zip (password: ☤ﮝﻻ⋩ﻛԷ따덕ڦ㏶쳥) contains another archive file called Firm.zip (password: ☃✧〠Ⓙ〶✰ǬⓆ). Unpack the file Reports.rar from Firm.zip and change its extension to exe. Then run it to install the program. If those passwords don't work just let me know. This hell was needed to prevent the installer from being deleted due to copyrights.
1.7.17 link:a704TV_1.7.17.zipHow to downgrade to 1.7.17:
Take out the hard drive and connect it directly to PC through ide adaptor.
Run "HD Clone"->Restore partition->choose the folder where 1.7.17 image is: first click on the needed drive from the left panel. Then using the right panel go to the folder with the needed image folder and click on it-> click Next (if the button is not active, it means you didn't choose the image)->in the next window "Target partition" click "Show all partitions" to uncover the hidden partition->find the hard drive of your Archos and click on the smaller partition called "unnamed". Its size has to be around 97MB->click Next->Start->Start copying->(Waiting)->Automatically->Quite HDClone.
Place the hard drive back into Archos and start it. Choose "repair" if recovery menu appears. You're DONE!
OS is 1.7.17 except the bootloader. Connect the hard drive to your Archos and start it. To downgrade the bootloader you will have to run the firmware file from my zip-archive. But I think there's no need for downgrading it as the HDD lockdown will not disappear like it would happen to 504 (possibly 404 and 604 too).
I'll be posting new info if I face it. Archos has stopped generating plugins, so there's no way of getting them except hacking. Therefore there's a lot of work to do.