Since you already have both networks to hand, you can add a full speed day pack to your current DTAC SIM in order to run tests using the router, including which bands you need to use for Carrier Aggregation. It won’t affect your current monthly package.
DTAC use Bands 1,3,28&40. You’ll be able to pair any combination of these. But you may need to check what is available at your location. If just Band 40 for instance, you may choose Band 40 + Band 40 as a pairing. DTAC upload is often considerably lower than it’s download offering, so check that at the same time. You can do the same with your AIS SIM.
AIS uses Bands 1,3,8 &41. Same as Truemove H.