After opening up the amp and making a sketch of the circuit, it's clear what is the main cause of the brightness some have found: the output coupling cap is grossly undervalued. It's 30uf. Most OTL amps come stock with at least a 100uf valued cap, though for the 300ohm HD600s so many use will be better served by a 220uf cap. So a common mod is to up that standard 100uf value.
With the 30uf cap and a pair of HD600s, that puts the corner frequency for the DV332 at over 17Hz. What you want is a corner frequency of about 2Hz, since phase shift is known to occur at up to about 10x the corner frequency, which would be 170Hz. It's no wonder that the mid-bass is anemic. With the mid-bass response anemic, for types of music with wide dynamic fluctuation (like orchestral), to hear the heart of the music (the midrange) in low volume passages, the amp's volume must be set high enough, but that then puts the more easily produced high frequencies into ear-bleed territory in the loud passages.
The first mod any DV332 owner not happy with the unit's sound ought to do is to replace that cap. I've now got the stock cap paralleled with a 220uf electrolytic. The sound is much, much improved. It's not the best solution -- the cap should outright be replaced to avoid the problems created by paralleling different types of caps of such similar value. Most reasonable here would be a 220uf electrolytic bypassed with a small-value film cap.
Why does the amp come stock with the wrong cap? Probably due to cost and pricing limitations, given the designer's desire to use a film rather than electrolytic cap. The stock cap is an SCR MKP cap. That is, it's a Solen film cap, which is of course a nice cap to use for audio signal applications. Retail they cost about $8US each. Even just a 100uf MKP cap can run 3 to 4 times that much money, not to speak of what a 220uf would cost. (And the 220uf wouldn't even fit in the chassis.) Adding that cost would significantly cut into what is already probably a pretty small profit margin, or would increase the retail price too much, making the DV amps much less appealing to the producers' target market.
The moral here is that an electrolytic of the proper value is a much better choice than a film cap of a horribly incorrect value. Even the folks at Bottlehead, who sure know what they're doing, supply their Crack OTL kit with an electrolytic for that output coupling cap.