Well, WAL are back in business themselves but I don't think their electronics are available separately.
The closest and most easily available preamp to the WAL filter preamp is indeed a John East design, but it was commisioned by ACG Guitars and is available and marketed by them - http://www.acguitars.co.uk/shop/inde...iewCat&catId=2
I have had an EQ02 5k in one of my basses for a couple of months now and it is incredible. It has the usual volume and balance controls but the tone shaping is taken care of by a "Bass Stack" and a "Treble Stack". The Bass Stack has a stacked knob where the lower ring controls the cut off frequency of the filter. If you twist it all the way anti-clockwise it only lets lower frequencies through, as you turn it clockwise it progressively lets higher frequencies through up to about 3K (I think). The upper knob on the stack allows you to apply a boost to the signal at the resonant frequency that you've set on the lower ring.
This, on it's own is very powerful, but then you also have the Treble Stack that works in almost the same way on the higher frquencies with the lower ring determining whether you just let the real high stuff through (10K) or let it go right down to 1K, with the same boost facility.
It takes a little while to get your head round compared to ordinary preamps, but it only took me a couple of days before it became completely natural to me. However, between these two controls I can get almost any sound I want (including getting my 6 string to make an indistinguishable tone from that of the bridge pup of my beloved Ric). All this power does have a very slight downside in that small tweaks to the pots can make a big difference to your sound but you soon get used to it.
I'm so impressed with it that I've just ordered another one, and upgraded to the EQ01 (the EQ02 is going in my fretless). This is essentially the same thing except that it's more powerful because it has a Bass Stack per pickup and a Treble Stack that is supplied by one or other pickup and selectable via switches on the board.
There is an EQ03 version which has even more power through having push/pull knobs to add mid controls but that's only available on ACG basses (along with some intriguing looking 'resonance pickups).
You can see those on the builders showcase in Luthiers Corner.
Can you tell I'm keen on them? I can feel an expensive habit forming through having to put them in all my basses...or alternatively, maybe I can sell some of my basses now because this preamp makes it possible for one bass to (very nearly) do it all.