Best amp for Onkyo D500 and Diatone DS32B

[bs Tubeman]

Hi all, I live in Vietnam where japanese gear are not hard to find. I recently have bought a pair Onkyo D500 and Diatone DS32B. I pair them up with a Denon 390 IV and they sound so good. But i feel that something is lacking.
And i found out that i want to bring the bass more.
I wonder what amp could be best for those babies.
Thank you all.
My stuff

 

[bs Tubeman]

Onkyo D500 Liverpool.

DAC and Bluetooth music Receiver.

Diatone DS 32B