The best hardware step sequencer in my opinion is the Cirklon (
www.cirklon.com), I use it to run my desktop Virus Ti and a Polar Ti2 - and everything else in the studio. No latency - perfect timing all the time, and up to 64 tracks.
Its not cheap but I think its excellent value - and if you have less to spend you could look for a 2nd hand P3 sequencer (made by the same fella).