Multichannel ecommerce ebay and amazon

Hi I am looking for someone who can create a multichannel ecommerce integration for my ebay, amazon and webstore. This would require order processing, order handling, shipping, inventory control off all stores in one place, accounts and integration shipping services with system.

Many off the shelf products on the web but I am looking for something more bespoke but also very similar to what people are offering.

please see following websites which are offering this kind of service to get an idea:

linnworks
brightpearl
channelgrabber
channelsupplier
giant systems


Thanks