I ended up using parcel force, booked it directly through parcel force website. It wasn't cheap, I think £50 or so including insurance up to £800.i also recently read ups (booked direct) sometimes are reasonable
As standard all parcels delivered in the UK get £25 free contents cover and international parcels get up to £50 contents cover for free. If the value of your contents is more than what comes as standard, then we offer extended cover of up to £1000 for both domestic and international deliveries. This option can be selected when placing your booking.
I used parcel hero, i scoured the excluded items of all the retail shipping brokers and Parcelhero seemed the best for 'amplifiers', their labels are the old style UPS ones but that's who I went with in the end.