the best 'tubey amp - warm,smooth,liquid' ?

I happen to have a sweet Mastersound 300b available.

Early, Which model do you have and what tube was it designed with (Vaic-KR)?

Zabiaud..If you are after that warm, lush, very smooth sweet sound then you should consider the tubes rather then the brand of the tube amp itself. There's a company out of China, called Psvane & Shuguang. Their tubes are made like tubes were in the late fifties and early sixties. With heavy filaments and thick envelopes. They are pricey but have a very long life. The tubes are beautifully cased in wood boxes. They are the best built tubes on the market.
Go to the Grant Fidelity website in Canada. They are the North America Distributor and you can buy direct. Again, these tubes have a very classic sound that was common fifty
years ago and are warmer and richer than other tubes of today. Some may find these tubes too warm and laid back and overly lush. but thats what I prefer personally so it all depends how much warmth your after.

I'd say it's more like EL84 based amps.

I wouldn't go with an off branded component. If you need that soft sound go for a Mac.