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Well Matrix make some brilliant Class A/B Rack mounted Power amplifiers. That Are very price competitive with the Other Brands

I have both. A Marshall 9005 EL34 Power Amp and a Harley Benton GPA - 400. The Tube Power amp is great for pre amps but will colour the sound so throwing in a Mesa or a Rev generator patch will change the eq curve of the amp so will not sound exact (EL34 have less bass add more mids) The Solid State Power amplifier is Not so coloured so amp models come out better and so Get the sound of the amp from the helix most authentically. On the plus side to the tube power amp it get rids of some of the digitall - ness of he amp. So yeah its all what you really want.

or Use an FX Loop block and rout the signal to a "send"

I have a HX-Stomp. and a Marshall 9005 50 watt stereo tube power amplifier. Because this is designed to take a Marshall Tube rack Pre-amp it will add power amp flavors to your sound, so i run just the pre-amp section of amplifiers. In My experience Marshall Style sounds work flawlessley and sound even better. But Mesa /Fender sounds lose some of their magic. still very usable but a Dual Rec doesn't have the Bass and Fenders lack high end Sparkle. But you can get an amazing Peavey 6534/ EVH 5150 El34 Sound using the Panama pre-amp. So It depends on what your are trying to achieve

I have a EHX Expression Pedal And it works perfectly They are around £40 in the UK