Preamp - 18 dB Gain too low?

1 to 2 o'clock is just fine, in fact it may be the best postition to get the maximum performance out of your pre-amps volume control.

26db was common when vinyl was king and low output phono pre-amps were used. Amps also had lower sensitivity. With the digital outputs are high (anywhere from 2v the standart I think to 6v), the pre-amp really no longer needs to add much if any gain at all. In fact many digital sources need no gain what so ever from the pre-amp, more probably some attenuation. Note all of the folks complaining that their volume is to high if the VC is higher than 8 or 9 o'clock. In a way you are blessed. :-)

Not a surprise for SET amp systems.

My guess with your 98 dB efficient speakers and your normal 18 dB preamp is that your power amp has voltage gain on the low side, probably to reduce tube noise coming from your speakers. As long as you are not getting too much noise from your system you should be fine with your preamp.