A very cheap, but quite good sounding, approach would be to build the Elekit 300b amplifier. Even if you don't have much in the way of soldering and other amplifier building skills, these can be learned on line and the it should be relatively easy to build if you go at it patiently.
A far more expensive alternative would be to buy the Synthesis A40 integrated amp with built in DAC. This is a 40 watt per channel amp that runs one of my favorite tube type (KT66). The built-in DAC is also quite good.
The Cornwalls sound very good with low-powered tube amps, whether modern or vintage. I would take advantage of its efficiency to utilize such amps because they tend to sound so much better than either solid state or high-powered tube amps. Of course taste varies, so I won't say that any particular amp is terrible. But, I will say that one should at least explore beyond the most popular options out there; look at options beyond Decware, Prima Luna and McIntosh.