balanced preamp

You might want to consider the Atma-Sphere MP-1 (2-box) or MP-3. Both can be ordered with a (absolutely sensational!) fully balanced differential 3-stage tube phonoamp. My amp is a McIntosh MC275 (tube) -- and since tube sound vs. ss sound is a function of the amp (and not the preamp, imo) your sonic result will be different.

I wouldn't make a selection using balanced as the most important factor to consider. I do feel its better but I would buy a component based on sound quality first. If it just happens to be balanced, thats OK too.

When I went to balanced connections with my ML 433 I was quite happy with the result. If a company goes to the trouble and expense of a fully balanced option, like your ML 336, it is likely to be the best option. But, just because a unit has XLR connections doesn't mean its fully balanced.

My ARC LS 27 and ML 433 sounded better even with cheap balanced cables than they did with expensive single ended.

Going internally balanced is a good way to reduce distortion of the circuit. This is true whether the preamp is tube or solid state.

If the balanced operation is done properly, the interconnect cables cease to be a part of the sound of the system, unlike single-ended. Note the caveat 'done properly'.

Although MANY great designers don't care about balanced operation (Conrad Johnson, etc.), I do. The solidity of XLR connections and the low noise/impedence has served me well in pro audio, and I was wondering aloud (here) about what was out there when the Kavent dude contacted me. I bought one of their S-33s (exactly the same preamp as a Vincent SA93, just different cosmetics) and am utterly amazed at how good it is, and it matches well with the XLR inputs on my Jolida 502p (and a Forte' 55 before that). Unfortunately the Kavent people have disappeared, but my preamp happily remains...a fully balanced design all the way through.