I see a lot of people comparing the new Ampegs to each other. Mostly they are doing side by side comparisons of the 4Pro, 6Pro and 8Pro. Just a word of advice here. If you ever include the 4Pro in your comparison MAKE SURE you use the correct bridged mono cable when you hook it up to the speaker and make sure the stereo/bridge button is IN. I hear people on forums and in reviews stating that the 4Pro was "weaker" or didn't have the same "punch" as a 6Pro for example... but they failed to realize that when they did their A/B of the two amps they used a regular 1/4" jack type speaker cable and moved it from one amp to the other during their comparison at the music store. What they are comparing is an 1,100 watt amp (6Pro is always an 1,100 watt amp into 4 ohms! It is a mono only amp!) to a 490 watt amp (the 4 Pro is only 490 watts into 4 ohms when you use a normal cable and don't have it set up for bridged mode). That is NOT a fair comparison. Set them up to run at the same wattage and you'll see that the 4Pro is more amp than the 6Pro and at 4 ohms it even sounds better than the 8Pro too! The 4Pro has the best EQ and tone shaping of the bunch. The parametric EQ's that Ampeg is using now don't have the same versatility as the 9 band graphic. You are limited to selecting only 4 frequencies to cut or boost. Yes, you can dial in any 4 you want...but only 4 bands. Try one... you'll see what I mean. You can't make a good sound decision on which one to buy reading other people's reviews. Few people working in music stores know how to correctly set up the amps so they are giving the correct (equal) wattage so you can demo them on an equal basis. Then the customer goes back home and writes in the various bass forums about how the 4Pro is inferior than the 6Pro or 8Pro... it's not. The problem is usually not having the 4Pro set up correctly... I guess you can tell I like the 4Pro... My tests today at Guitar Center told me that the 4 offers the most tone shaping, versatility (stereo or mono or bridged mono or Bi-Amp), And has a clearer overall tone to my ears using the same speaker and bass during the test (the others were fundamentally bassier with the same approximate settings) especially on the D and G strings. And I also learned that the Tube Voltage knob on the 6Pro does little to affect the sound. The change is very subtle. It was subtle on my 3Pro and it is still subtle on the 6Pro...definately not a feature to sway me towards the 6. I have two 4Pro's... I'm keeping them.