753 need big current amplification. They were never recommended to go with Audiolab back in the dim and distant, even with 8000M.
I run mine with a large efficient Japanese amplifier and they work much better. Even a Quad 606 didnt do so well. And steer clear of the freedom versions.
They were a very good speaker for the money, folded one piece box, multi lightweight drivers giving the equivalent of a large surface area and a pretty high efficiency of 89 to 90db and a reasonable 6 ohm load.
There was little to touch them at that price bracket. I had access to a hell of a lot of speakers from all corners and to do better I needed to look at PMC or some others (I forget their names now). Contemporary B&W, Kef, Tannoy werent cutting it at the time unless you went for higher models.
Unfortunately Mission are no more and its just a brand name churned out in China under the IAG group along with Wharfedale, Quad and Audiolab.