I give you three that I have used in the past year and recommend all of them.
GSP 1101
Rocktron Xpression
Axe FX
All three of the units are pretty true to the amps tone and that’s why I like them all!
(GSP 1101) 4 cable method, PC editor (through MIDI) this processor I find a little unique the quality of the effects are awesome as far as programming the effects very easy not as much to tweak as other processors. When programming an effect, it is like somewhere between a stomp box and a full blown processor. As for the 4CM the unit is arranged in such a way stomp box models , compressor are all before the preamp section, delays and reverbs would be after the preamp, however the chorus flanger phase type effects you can change weather you want it after or before the preamp. Although other have had problems with noise mine has always been quiet. The unit also has amp models which I never really got into.
(Rocktron Xpression) Awesome sounding unit! This unit does not have any models it is basically all time based effects and compression. There is no 4CM and no PC editor (and there won’t be one, I have inquired) As far as programming there is more detail than the GSP 1101, the interface is a bit old school takes a little to get use to. Sounds like I am slamming the unit but I’m not, just different. The end result is worth the little extra time you may have to spend with the unit. I do have one complaint the “reverb” its sound great but it is very generic in programming there are no small rooms or large halls I really wish this unit had the reverb of its older brother the Intellifex. Killer delays and chorus flanger & phase I personally prefer this unit over a G-Major, which does have a better reverb.
(Axe FX) Much bigger price tag than the other two. This unit is famous for its amp models but let’s keep it an effect processor for this topic. 4CM, PC editor. Very in depth programming, you also have to pay close attention if the unit does not sound right to you or something sounds a bit colored, you need to check your setup. When doing the 4CM, unlike the GSP 1101 you can place any effect on either side of the preamp (but I think the GSP 110 placement is perfect as is) The quality of the effects reflect its price tag, In fact it’s a good deal , the effects are stellar! I would pay the money just for the effects.
All three units are midi friendly