Lewm, the only reason people might think the bass has no oomph is that their tonearm's effective mass is too low. Koetsu's have plenty of oomph but they require a rather heavy arm or some ballast to do their best.
Michael, there are two basic Koetsu chassis, the regular one and the platinum magnet version which I think is a little more detailed. I think the Rosewood Signature Platinum is the hot point in the line. I know of no one who thinks Koetsu's sound bad. I have not heard one with Harbeths but I can not imagine it wouldn't sound great as long as you make sure your tonearm's effective mass is up there where it should be. The Stone body versions will work better in lighter arms as they are quite heavy. Try as I might I can not hear much difference between the ones I have heard. I do not think IMHO they are worth the money. Having said all this if you are spending anything around $4000 you really should give the Ortofon Windfeld Ti a close look. It is not as warm as a Koetsu but it will sail through tracks that the Koetsu stumbles on. There is no cartridge that tracks as well as the Windfeld that I know of. It is perfectly neutral and plays everything well from string quartets to Metallica. I use my Koetsu mostly for classical and female voices. I also have a Clearaudio and an Air Tight. The Windfeld Ti is handily the best all round cartridge of them all because of it's neutrality and tracking ability. There are situations the other cartridges might make me unhappy but never the Windfeld.
Michael, there are two basic Koetsu chassis, the regular one and the platinum magnet version which I think is a little more detailed. I think the Rosewood Signature Platinum is the hot point in the line. I know of no one who thinks Koetsu's sound bad. I have not heard one with Harbeths but I can not imagine it wouldn't sound great as long as you make sure your tonearm's effective mass is up there where it should be. The Stone body versions will work better in lighter arms as they are quite heavy. Try as I might I can not hear much difference between the ones I have heard. I do not think IMHO they are worth the money. Having said all this if you are spending anything around $4000 you really should give the Ortofon Windfeld Ti a close look. It is not as warm as a Koetsu but it will sail through tracks that the Koetsu stumbles on. There is no cartridge that tracks as well as the Windfeld that I know of. It is perfectly neutral and plays everything well from string quartets to Metallica. I use my Koetsu mostly for classical and female voices. I also have a Clearaudio and an Air Tight. The Windfeld Ti is handily the best all round cartridge of them all because of it's neutrality and tracking ability. There are situations the other cartridges might make me unhappy but never the Windfeld.