I have no hands on experience with any unit post H3000 so I am unaware of what tangible advancements each successive model introduced. So unfortunately when you state how much better could the 4000 be I honestly don’t know. As you suggest the 7600 would certainly be the most modern and after skimming the product details it’s more powerful than the initial 7000 series which that is stated as being 4x the processing capabilities of the DSP4000.

One thing I hadn’t given enough thought on is the going price of the 7600, looking at eBay the past few days the prices are right up there and approaching the 9000 territory so perhaps a 7600 isn’t the best bang for buck. On the other hand with it being recently discontinued the chances of getting a perfectly working unit would theoretically be much greater than an original 7000 series or a 4000 series unit seeing as those are much older.