Volume issues moving from Mix Plus to HD

[brotone]

I hope I'm in the right forum and not asking an oft-answered question.
I am finally moving from my trusty old Mix Plus system to a new HD1 rig (systems listed below).
My first big problem: when I open existing 6.4.1 sessions in the new HD rig, volume levels are through-the-roof loud. Everything, each individual track plus the master out, red-line like crazy.
I have taken these same 6.4.1 sessions to another HD studio (running 7.3, I think) and had them open fine.
I confess to being confused about calibrating converters. When I switched from +6 session to +12 sessions, I wasn't exactly clear on what was going on, and I didn't recalibrate anything. Much searching came up with no clear explanation, but I forged ahead anyway, working with what to me sounded like much quieter mixes, but things were still acceptable and dealable. Now I have a used 192, a new computer and HD1, and volume issues. I have not ventured into recalibrating the 192 yet (haven't found an external VU meter, but that's for a different thread, I think).
One other possibly pertinent bit of info: it has happened sometimes in the Mix system that moving around plug-ins, especially adding or converting RTAS plugs, can cause the whole mix to jump up about 12db in volume. Saving, quitting, restarting ProTools and reopening the session returns things to normal. The Mix cards check out AOK w/ Digitest. I haven't tested the new rig yet (my next move).
If anyone recognizes this situation and has anything to offer - information, suggestions, resources, whatever - I would greatly appreciate it.

Thanks in advance,
brotone

Systems -
Old Mix Plus: PowerMac G4 MDD Dual 1.25, OSX 10.3.5, PT 6.4.1, Apogee AD-8000.
New HD1: Mac Pro 8-core 2.85, OSX 10.5.4, PT 7.4.2, 192i/o w/ extra a/d card.

[the dude]

this was fixed back in 2005

Did you ever install any of the cs Updates for 6.4.1

Includes fixes from Pro Tools TDM 6.4.1cs1:

Fixed: When Using Pro Tools in +12 dB Fader Gain Mode, the Level on Outputs Could Be Incorrectly Increased by Up to18 dB (Item #54461)


Pro Tools TDM 6.4.1cs4 for Mac OS X contains the following:

Volume level compatibility with pre-Pro Tools 6.4 versions of Pro Tools is maintained for all volume levels below +6 dB.
Any volume levels written above +6 in a +12 dB session will play properly in Pro Tools 6.4 or later. Volume data written above +6 dB will be truncated (moved to +6 dB) if the session is opened on a pre-6.4 version of Pro Tools This is the same behavior as all versions of Pro Tools 6.4 and later.

[brotone]

Thanks for the reply, Dude. I am not sure if I've installed those updates, and I won't be able to check for a couple of weeks (on the road right now), but I will definitely check it out when I get back. I appreciate your time and knowledge.

And I gotta say, I loved your rolling against Quintana in the semi's.

brotone