Mosfet source resistor value?

[kacernator]

Hi,

I have built this mosfet power amp, it is being driven by tube preamp. Sounds good, but my questions are about mosfet source resistors. What value should be chosen? When I go higher in value (0.47 Ohm) sound is more in the mids and not so big soundstage. When I lower them (0.1 Ohm) soundstage is lot bigger, more and deeper bass, but overall sound is muddier. I also experimented with different types of resistors. I have found that most ordinary 5W ceramic resistors sounds awfull in this position - that surprised me a little, because I see lots of folks here use them. Second best were metal oxide and metal film.

So what source resistor value should be chosen? Lower as possible and if sound is muddy then the problem lies somewhere else in amplifier?

Thank you.
Standa.