Hafler XL600 Vs Hafler 9505 Much difference?

Hello all, I am new here and still learning to navigate the website. I have been out of audio for a number of years. I had an old Hafler XL600 years ago and really liked it for the price. I am thinking of getting into audio again and am considering purchasing either an XL600 or the newer Hafler 9505/9500. I have read there have been a lot of improvements in amplifiers in the last decade. Is that true? How much difference is there in the amps I am refering to? Would I notice a difference between the XL600 and the newer amp? I hope to purchase Boston Acoustics VS336 speakers to go with this.
Any info would be helpful.
Thanks