Why are you and he together at all?. I realise you love him etc but this is really no life for you nor your child. You are already sadly enabling this for the sake of your child, an action she will not thank you for doing either. Children of hoarders also have a very hard time of it at home.
I would do a lot more reading around this subject because you do seem woefully informed as to what hoarding actually is and entails not just for the hoarder but for family members. You cannot help him or rescue him but you can certainly help your own self here.
Its not just amazon packages though is it?. You mention round wires/ recording desks/ boxes etc along with this comment, "His “studio” has become a real mess -I mean tables up turned on their sides, way too much furniture recording equipment up to your shoulders when you walk in, 100 cardboard boxes, old biscuit tins, bags and bags of bubble wrap".
"He has a shed in the garden that is literally floor to ceiling packaging materials “in case he sells something”
You committed the cardinal sin in his eyes to touch and otherwise disturb his hoard by moving or otherwise clearing any of it.
Hoarding is classed as a mental illness and you seem ill equipped yourself re understanding what this actually is along with the effects of same on the wider family; in this case your DD and you. His hoard is all encompassing to him and it will effect you and your DD to its detriment if it is not already doing so.
Hoarding is a disorder that may be present on its own or as a symptom of another disorder. Those most often associated with hoarding are obsessive-compulsive personality disorder (OCPD), obsessive-compulsive disorder (OCD), attention-deficit/hyperactivity disorder (ADHD), and depression.
Although less often, hoarding may be associated with an eating disorder, pica (eating non-food materials), Prader-Willi syndrome (a genetic disorder), psychosis, or dementia.
Those who hoard usually experience embarrassment about their possessions and feel uncomfortable when others see them. They have clutter, often at the expense of livable space, feel sad or ashamed after acquiring additional items, and they are often in debt.
A lack of functional living space is common among hoarders, who may also live in unhealthy or dangerous conditions. Hoarders often live with broken appliances and without heat or other necessary comforts. They cope with malfunctioning systems rather than allow a qualified person into their home to fix a problem.
I would end this relationship; its not working out now and it will only go further downhill for you and your child if you choose to stay with him. You have a choice re this man, she does not.