The Aspire lounge, like the BA lounge is in the non Schengen area and is opposite the BA lounge. Both are accessible after clearing passports and before clearing security, which currently is at the gate in Schiphol. So you can follow the instructions in the BA AMS lounge thread for how to get there, including photos and a map, but it is essentially the same invigorating trip across the rooftop. They are both some distance from the BA gate, but if you have checked luggage it's not such a big diversion.