Vic...I just noticed this - even in the living room!
Last night when I hooked everything up, I had the cab solid on the floor. Very full sound and not bright or crispy.
Today, I put it back on top of my sideways twin and - BAM - much brighter and more high end, but still full. I took a few minutes to crank up the twin to about 6 and the mac to about 4, lowered my volume knob on my guitar and dialed in the tone with my guitar's tone knob. For some licks/songs it sounded perfect with the tone wide open, some sounded better with the tone rolled off a bit.
One thing I noticed was that when playing with my tone knobs on my guitar using the mac, there are a few sweet spots that add in certain frequencies or harmonics that really nail the tone. Above or below those spots and it sounds more "normal".
Then i kicked on my od and wow! the mac really reacts differently than just the twin.
I had to dial down my tone knob to almost all the way gone and then that sweet Jerry harmonic overdrive kicked in! I had never been able to get this kind of sound just with the twin! The tone knob is reactive and really makes a difference like never before. When just playing the twin, the tone knob was just two settings, muddy and clean. I remember reading on the yahoo boards about how Jerry would roll down his tone knob to get a horn like OD going - I never understood that or had it work for me until today.
So I found that I can set the volume levels higher on the twin and mac and roll down the volume on the guitar to find the right level - then I play with the ton knob on the guitar till I get the right quack. Adding more volume on the twin gives more more tube breakup and I can easily control the breakup with pick dynamics.
Adding the Mcintosh is like having a whole new rig! Now I just need to save up enough for the Sarno sms!