Here’s some info from another forum
Spider IV 75 a Great Product Made Even Better Based on Extensive Market Research & Line 6 Insight!
SPIDER III: WHAT WORKED
Unmatched Range of Tone with Line 6 Amp Models from Clean to Insane
Smart Control FX Are Easy to Dial In and Sound Great
Instant Rock Star Connection via Hundreds of Artist and Song-Based Presets
Universal Praise for Spider III’s Look
SPIDER IV: WHAT’S DIFFERENT?
Better Sounding and Better Feeling Amp Models Using Revamped Line 6 Modeling Technology
Total Control of Better Sounding FX, Use Smart FX Interface or Dive Deep into FX Parameters
Newly Remastered Artist and Song-Based Presets with Improved Preset Navigation
New Black Aesthetic Connects to Spider III But Now Vibes More Pro
SPIDER IV FEATURE
16 Revamped Amp Models – Benefit: Experience better sounding and better feeling amp models, ably handled by a SHARC processor. Amp models are based on the top-selling POD®X3, and optimized for Spider IV.
Total Control of 20 FX – Benefit: Use the familiar Smart FX interface for instantly inspiring FX tones from POD X3, or choose to dive deeper and tweak up to 6 FX parameters. Route any effect Pre or Post for unmatched flexibility.
New Artist Presets and Improved Preset Navigation – Benefit: Spider IV offers over 250 killer presets dialed in and approved by real Rock Stars. We also added a bigger LCD display and improved the menu navigation.
On-Board Looper and Other Premium FX – Benefit: Loop to your heart’s content, or go crazy with our new intelligent harmonizer, pitch shifter, and auto-wah. Get even greater control with FBV.
Improved Direct Out Sound Quality – Benefit: Many of our customers use computers to record, and Spider IV delivers a POD X3 quality solution with Spider’s ease-of-use.
Seamless FBV Integration – Benefit: FBV Foot Controllers make it easier to practice and perform, add additional FX like Volume/Wah, and are an easy up-sell.
Upgradeable Amp Platform via FBV Mk II – Benefit: FBV Mk II Foot Controllers feature USB connections that will allow for future firmware upgrades.
Ive highlighted the important improvements. If this proves to be a scaled down podx3 with the most impt models with a speaker, its gonna rock. Of course since this isn’t official yet, there may be some inaccuracies.