Should I go for sub-woofer or new speakers?

I'll second the REL subwoofer recommendation. Their subs do well with music and seem to easily integrate into a system. I'm not familiar with the Royd speakers, but when I have used a sub with bookshelf speakers, better results were usually obtained by placing the sub between the speakers, setting the sub's crossover point as low as is feasible and not cranking the sub level up too high.

As for power cords, note that the Ikemi has a switching mode power supply. So-equipped components don't seem to be greatly changed by power supply tweaks in my experience. I tried a few power cords when I had an Ikemi. Most seemed to make no difference in the sound. I thought that there were perhaps some very subtle improvements with the modestly priced Audusa Eupen cables however. Sorry, but I don't have any experience with cables and Naim gear.

There are a lot of good subs, and a lot of good reasons to use a sub/monitor combo. I use an M&K MX700 which, like most M&K subs, is controllable and can "get out of the way" of your beloved monitors. Borrow a sub if you have to, but you should really give one a try.

Charlie

I would also recommend the REL Strata III, an excellent sub. I doubt you could equal its performance by adding $800 to whatever you could get for your existing speakers. Just be sure you are willing to spend the time and effort to get it set up properly. It's not rocket science but does take some time.

I sometimes use my sub with my small apogee ribbons and it does give them that full range sound and is very nice change of pace with them. As Thsalmon says,works best if sub is placed between the speakers. In my case,between,to the right and a little bit back of the mains. Hometheater placement does not seem to matter as much which is where my sub is used the most. The REL or M&K's might just do it for you,they are both very good and fast subs.

I thin u answered your own question...you like what own...and want more bass...wah-la...subwoofer...and for $500...the HSU vt-2 would be the one to checkout...I also hear Aidre has a good one also...at $400...you could spend more...but these are half the price of anything approaching musical sub sound...