Hifiman + LD is great sounding combination. There is no bass roll off and there is power more than enought. OTL is not designed for these, but in this case perfect match! If I remember right only he400 series sounds great using LD.

What tubes would be best option when using hifiman 400i (35 ohms) with LD 3? Now using standard power tubes with mullard cv4010 and sounding great. 6N6P-IR + 6HM5? 6SN7 not compatible with low impedance? Or should I try, 400i are quite easy to drive.