does high end system need expensive speaker cable

Speaker cables are no less important than interconnects. Yours are both insufficient. You don't yet really know what your system is capable of.

NO. Expensive doesn't always mean better.

Speaker cables can make a difference, both good and bad, and cost doesn't have a great deal to do with the result (IMHO). I think many folks use cable as a form of tone control to correct deficiencies in their basic electronics/speaker match, not to allow the signal from the amp to pass thru to the speaker with a minimum of change. Personally I would focus is on getting short runs of cable with the matching impedence/capacitance to your speakers. A cheap experiment - buy a couple of short runs of 8 - 10 guage twisted copper wire (50 cents a foot) and use them as a reference to how other cables sound in comparison, then decide if you are willing to pay for the difference. A caveat with cables - don't do short listening comparisons, let them play, or just rest, in the system for about 24 hours before you sit down to listen to them. You might be surprised - some cables that seem to shine in side by side comparisons can be down right irritating in long term listening.

Be careful, its a jungle out there!

Just want to let you know about something that I went through when I purchased the Nordost SPMs for my system (interconnects & Speaker wire) and a thing sounded good, the soundstage opened up very nicely, the midrange was smooth and so open. At that time I thought I was in Heaven. But after a while I notice that the highs just didn’t sound right. They sounded restricted, and the Dyns are known for their detailed highs. At that time I just wrote it off, as the Dyns just weren’t that good because SPM Cable is suppose to be a great cable. Then one day I was just playing around with Levinson’s CZ Gel interconnect cable that I never used and notice right after the 1st record that there was way more bass in the music and the high were endless.
I say all this to let you know IMHO you are missing a hold lot I now have Valhalla and it like night and day compared to SPM, and it has to be a big jump from Red Dawn.

Like Timo, I agree that more expensive cables does NOT imply better sonics &
Like Inna, I agree that right now you don't know what your system is capable of. Just reading the list of components tells me that you *should* be able to create a grand sonic experience that comes closer to reality than many, many other systems out there. Do you feel that you have an awesome sonic experience every time you sit & listen?? If not, then you are missing something: your components are not synergistically matched, you might be skimping on speaker wires, you might have the wrong combination of interconnects & speaker cables, your room might need treatment, you might need better isolation, etc, etc. Since you make no mention of your setup environment, people cannot guide you: whether you need better speaker cables or something else.

What high quality speaker cables bring to the table are:
* ultra low resistance.
* good/superlative insulation material (aero-PE, teflon) such that the capacitance/ft. is minimized.
* very low inductance.

Having high resistance in the cable has an adverse effect on the bass quality - it becomes flabby, loses its punch & it'll overstay its welcome in the room.
High capacitance *might* cause a lesser amp to oscillate (i.e. become unstable) but I doubt that the FPB400 will be perturbed.
Having high inductance can cause high freq. roll-off & this roll-off can be disproportionate across the 10K-20KHz range i.e. it could be more in one area vs. another.

The above listed effects are not exhaustive & shows what *could* happen when some cable electrical parameters are on the excessive side. Note that most reasonably constructed cables already have very low R, C & L & so when comparing these electrical charac. one is comparing a few tenths or hundredths here & there - it's all RELATIVE. You might be asking if a few tenths or hundredths here & there makes a difference? My personal experience says that it most certainly does! However, YOU should listen to a few brand names & convince yourself. You'll find that cable insulation, litz or not, single strand or multi-strand, thick gauge vs. thin gauge will make a diff. albeit subtle. You'll have to draw the line by looking at your budget.

It is not always true that the more expensive the cable, the more merits it has w.r.t. the qualities listed above. However, most of the time, more expensive cables have much better quality of parts that leads to having better electrical characteristics than a cheaper cable.

Having said all this, electronics & cables is a synergistic match 8 or 9 times out of 10. Just 'cuz one has the best electrical charac. in a cable doesn't mean it'll have the best sound in YOUR system! The unfortunate truth, I'm afraid! You'll have to try various cables before you settle on one than does better than the Red Dawn. Then again, your audition might show that the Red Dawn is the best for your system. Tough for me to say.

So, there IS a jungle out there w.r.t. cables so start looking @ cables that others have used with Krell gear. I have seen Krell being used a lot with MIT cables. This might be a good place to start. I think that Transparent cables & MIT have the same origins & so Transparent cables will be another to look at.
FWIW. IMHO.